DOCSLIB.ORG

Actin-Troponin-Tropomyosin Complex (Muscle Relaxation/Cooperativity/Regulated Actin) Lois E

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Actin-Troponin-Tropomyosin Complex (Muscle Relaxation/Cooperativity/Regulated Actin) Lois E Proc. Nati. Acad. Sci. USA Vol. 77, No. 5, pp. 2616-2620, May 1980 Biochemistry Cooperative binding of myosin subfragment-1 to the actin-troponin-tropomyosin complex (muscle relaxation/cooperativity/regulated actin) Lois E. GREENE AND EVAN EISENBERG Laboratory of Cell Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20205 Communicated by Terrell L. Hill, February 22, 1980 ABSTRACT The binding of myosin subfragment-1 (S-i) to of a few S-1 molecules, free of ATP, to the actin filament and the F-actin-troponin-tropomyosin complex (regulated F-actin). pushing the tropomyosin away from its inhibitory position, thus was examined in the presence of ADP (ionic strength, 0.23 M; preventing inhibition of the ATPase activity even in the absence 220C) by using the ultracentrifuge and S-1 blocked at SHI with iodo["4C]acetamide. S-1ADP binds with positive cooperativity of Ca2+. Cooperative responses have also been observed in the to regulated F-actin, both in the presence and absence of cal- presence of Ca2+. Weber and coworkers (6) found that at high cium; it binds independently to unregulated actin. With and S-1 concentration the ATPase activity of regulated acto-S-1 can without CaO+ at very low levels of occupancy of the regulated be potentiated so that it is higher than the ATPase activity of actin by S-19ADP, S-1*ADP binds to the regulated actin with acto*S-1 in the absence of troponin-tropomyosin. <1% of the strength that it binds to unregulated actin, whereas The cooperative responses observed with regulated actin are at high levels of occupancy of the regulated actin by S-1-ADP, S-1ADP binds about 3-fold more strongly to the regulated actin fundamental to our understanding of the biochemical basis of than it does to unregulated actin. The major difference between regulation. Up to the present time, there have not been any the results obtained in the presence and absence of Ca2+ with studies on the binding of S-1 to regulated actin in the absence regulated actin is that, in the absence of Ca2+, the binding of of ATP. Equilibrium binding studies are generally easier to S-1'ADP remains weak until a higher free S-1ADP concentra- interpret than steady-state ATPase studies. Therefore, in the tion is reached and the transition to strong binding is much more present study, using a method previously used in our studies on cooperative. These results are consistent with a model that is basically similar to the cooperative binding model of Hill [Hill, the binding of S-1-nucleotide complexes to unregulated T. L. (1952)1. Chem. Phys. 20,1259-12731 and of Monod et al. F-actin (7), we investigated the binding of S-1-ADP to regulated [Monod, J., Wyman, . & Changeux, J. (1965)1. Mol. Biol. 12, F-actin both in the presence and in the absence of Ca2+. 88-118]: The regulated actin filament can exist in two forms, At ionic strength = 0.23 M at 220C, although S-1-ADP binds a weak-binding and a strong-binding form; and Ca2+ and independently to unregulated actin, it binds with positive co- S-1.ADP, acting as allosteric effectors, shift the equilibrium operativity to regulated F-actin, both in the presence and ab- between the two forms. sence of Ca2+. With and without Ca2+ at very low levels of It is now generally accepted that muscle contraction is caused occupancy of the regulated actin by S-1-ADP, S-1-ADP binds by myosin and actin filaments sliding past each other as ATP to the regulated actin with <1% of the strength that it binds to is hydrolyzed. In skeletal muscle the regulation of muscle unregulated actin, whereas at high levels of occupancy of the contraction appears to be controlled by the troponin-tro- regulated actin by S-1-ADP, S-1-ADP binds about 3-fold more pomyosin complex which binds to the actin filament to form strongly to the regulated actin than it does to unregulated actin. regulated F-actin. The most widely accepted mechanism of Our results are consistent with a typical cooperative binding troponin-tropomyosin action is the steric blocking model (1-3) model (8-10) in which the regulated actin filament can exist which suggests that the position of the tropomyosin molecule in two forms, a weak-binding and a strong-binding form. Ca2+ on the actin filament controls the actin-myosin interaction. This and S-1-ADP, acting as allosteric effectors, shift the equilibrium model proposes that, in the absence of Ca2+, tropomyosin takes toward the strong form. a position where it blocks the binding of myosin to the thin MATERIALS AND METHODS filament whereas, when Ca2+ binds to troponin, the tropomy- osin is thought to move toward the central groove of the actin Rabbit skeletal myosin, S-1, and actin were prepared as de- filament, enabling the myosin to interact with actin. Because scribed by Stein et al. (11). The troponin-tropomyosin complex the tropomyosin molecule spans seven F-actin monomers (4), was prepared according to Eisenberg and Kielley (12). The the position of the tropomyosin is thought to be effective over molecular weights used for S-1, actin, and troponin-tropomy- the entire actin unit and, therefore, this model suggests that osin complex were 120,000, 42,000, and 150,000, respectively. cooperativity is an inherent part of regulation. Protein concentrations were determined by UV absorption and On a biochemical level, the removal of Ca2+ from the tro- the following extinction coefficients: 750 cm2/g at 280 nm for ponin-tropomyosin complex generally causes marked inhibition S-1, 1150 cm2/g at 280 nm for F-actin, and 380 cm2/g at 278 of the actomyosin ATPase activity. However, this is not always nm for the troponin-tropomyosin complex. The rabbit myosin the case, as was observed by Bremel and Weber (5). At low ATP was labeled with iodo['4C]acetamide, as described (13), re- concentration and high ratios of subfragment 1 of myosin (S-i) sulting in 1 + 0.1 mol of iodoacetamide incorporated per mol to actin, they found that the ATPase activity of regulated of S-1. actin-S-1 complex (acto-S-1) is no longer sensitive to Ca2+. They Binding studies were conducted in the preparative centrifuge suggested that this cooperative response was due to the binding (Beckman L2-65B). The SHI-blocked S-1 and regulated actin in a total volume of 4 ml were stirred for several minutes and The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "ad- Abbreviations: S-1, subfragment 1 of myosin; acto-S-1, complex of actin vertisement" in accordance with 18 U. S. C. §1734 solely to indicate with S-1; EGTA, ethylene glycol bis(f-aminoethyl ether)-N,N,- this fact. N',N'-tetraacetic acid. 2616 Downloaded by guest on September 28, 2021 Biochemistry: Greene and Eisenberg Proc. Natl. Acad. Sci. USA 77 (1980) 2617 then allowed to remain for 30 min at 220C before centrifuga- Scatchard plot shows a marked convex curvature, indicating tion. All binding studies were conducted at ionic strength 0.2 that the binding of S-i ADP is highly cooperative in the absence M and 220C in the presence of 2.5 mM ADP to saturate both of Ca2. the S-1 and acto-S-1 with ADP. Diadenosine pentaphosphate This cooperativity is shown more clearly in Fig. lB where (3 ,M) was added to inhibit myokinase activity. The order of the fraction of actin saturated with S-I is plotted as a function addition of the proteins typically was actin, S-1, and then the of free S-1 concentration. In contrast to the situation with un- troponin-tropomyosin complex. Aliquots (3-ml) were then regulated actin, at a free S-1 concentration less than 1 ,M there centrifuged for 1 hr at 80,000 X g. An 0.5-ml aliquot removed was almost no binding of S-1iADP to regulated actin. Then, over prior to centrifugation and the supernatant after centrifugation a narrow range of S-1 concentration (1 to 1.5 MM), the fraction were assayed for radioactivity in a Beckman LS-250 liquid of regulated actin saturated with S-I increased from about 0.05 scintillation counter to determine the total and free S-1 con- to 0.5 which is about twice the level of saturation observed with centrations, respectively. In the absence of actin, >97% of the unregulated actin at 1.5 MM S-1. Finally, above a free S-1 S-1 remained in the supernatant after centrifugation. Cen- concentration of 1.5 MM, the binding of S-1 to regulated actin trifugation of the actin alone showed that >96% sedimented, no longer was cooperative but was about 3 times stronger than as determined by absorbance. The binding data were plotted the binding of S-I to unregulated actin. This can best be seen by using the Scatchard equation (14) and the value of the slope by comparing the slopes of the Scatchard plots for regulated for linear regions of the Scatchard plots was determined by and unregulated actin at 0 > 0.5 in Fig. IA. linear regression analysis. In general, for cooperative binding systems, noncooperative ADP and diadenosine pentaphosphate were from PL Bio- regions of binding occur at both very low and very high levels chemicals and iodo[14C]acetamide was from Amersham. of saturation and, therefore, binding constants can be obtained for these regions.
Load more

Recommended publications
  • Appropriate Roles of Cardiac Troponins in Evaluating Patients with Chest Pain
    J Am Board Fam Pract: first published as 10.3122/jabfm.12.3.214 on 1 May 1999. Downloaded from MEDICAL PRACTICE Appropriate Roles of Cardiac Troponins in Evaluating Patients With Chest Pain Matthew S. Rice, MD, CPT, Me, USA, and David C. MacDonald, DO, Me, USA Background: Diagnosis of acute myocardial infarction relies upon the clinical history, interpretation of the electrocardiogram, and measurement of serum levels of cardiac enzymes. Newer biochemical markers of myocardial injury, such as cardiac troponin I and cardiac troponin T, are now being used instead of or along with the standard markers, the MB isoenzyme of creatine kinase (CK-MB) and lactate dehydrogenase. Methods: We performed a MEDLINE literature search (1987 to 1997) using the key words "troponin I," "troponin T," and "acute myocardial infarction." We reviewed selected articles related to the diagnostic and prognostic usefulness of these cardiac markers in evaluating patients with suspected myocardial infarction. Results: We found that (1) troponin I is a better cardiac marker than CK-MB for myocardial infarction because it is equally sensitive yet more specific for myocardial injury; (2) troponin T is a relatively poorer cardiac marker than CK-MB because it is less sensitive and less specific for myocardial injury; and (3) both troponin I and troponin T may be used as independent prognosticators of future cardiac events. Conclusions: Troponin I is a sensitive and specific marker for myocardial injury and can be used to predict the likelihood of future cardiac events. It is not much more expensive to measure than CK-MB. Over­ all, troponin I is a better cardiac marker than CK-MB and should become the preferred cardiac enzyme when evaluating patients with suspected myocardial infarction.
    [Show full text]
  • Familial Adenomatous Polyposis Polymnia Galiatsatos, M.D., F.R.C.P.(C),1 and William D
    American Journal of Gastroenterology ISSN 0002-9270 C 2006 by Am. Coll. of Gastroenterology doi: 10.1111/j.1572-0241.2006.00375.x Published by Blackwell Publishing CME Familial Adenomatous Polyposis Polymnia Galiatsatos, M.D., F.R.C.P.(C),1 and William D. Foulkes, M.B., Ph.D.2 1Division of Gastroenterology, Department of Medicine, The Sir Mortimer B. Davis Jewish General Hospital, McGill University, Montreal, Quebec, Canada, and 2Program in Cancer Genetics, Departments of Oncology and Human Genetics, McGill University, Montreal, Quebec, Canada Familial adenomatous polyposis (FAP) is an autosomal-dominant colorectal cancer syndrome, caused by a germline mutation in the adenomatous polyposis coli (APC) gene, on chromosome 5q21. It is characterized by hundreds of adenomatous colorectal polyps, with an almost inevitable progression to colorectal cancer at an average age of 35 to 40 yr. Associated features include upper gastrointestinal tract polyps, congenital hypertrophy of the retinal pigment epithelium, desmoid tumors, and other extracolonic malignancies. Gardner syndrome is more of a historical subdivision of FAP, characterized by osteomas, dental anomalies, epidermal cysts, and soft tissue tumors. Other specified variants include Turcot syndrome (associated with central nervous system malignancies) and hereditary desmoid disease. Several genotype–phenotype correlations have been observed. Attenuated FAP is a phenotypically distinct entity, presenting with fewer than 100 adenomas. Multiple colorectal adenomas can also be caused by mutations in the human MutY homologue (MYH) gene, in an autosomal recessive condition referred to as MYH associated polyposis (MAP). Endoscopic screening of FAP probands and relatives is advocated as early as the ages of 10–12 yr, with the objective of reducing the occurrence of colorectal cancer.
    [Show full text]
  • Alpha-Actinin-3 R577X
    Annals of Applied Sport Science, vol. 4, no. 4, pp. 01-06, Winter 2016 DOI: 10.18869/acadpub.aassjournal.4.4.1 Short Communication www.aassjournal.com www.AESAsport.com ISSN (Online): 2322 – 4479 Received: 20/03/2016 ISSN (Print): 2476–4981 Accepted: 10/06/2016 Alpha-actinin-3 R577X Polymorphism Profile of Turkish Professional Hip-Hop and Latin Dancers 1,2 * 1 1 2 1 1 Korkut Ulucan , Betul Biyik, Sezgin Kapici, Canan Sercan, Oznur Yilmaz, Tunc Catal 1Üsküdar Univerity, Haluk Turksoy Sok. No:14, Altunizade, Üsküdar, İstanbul, Turkey. 2Marmara University, BAsibuyuk Yolu 9/3 MAltepe Saglık Yerleşkesi, MAltepe, Istanbul, Turkey. ABSTRACT Actins are small globular filaments functioning in cell processes like muscle contraction, and stabilized to the sarcomeric Z- discs by actin binding proteins (actinins). One of the important gene coding for actin binding proteins in fast twitch fibers is alpha- actinin- 3 (ACTN3). In this research, we have conducted a gene profile study investigating the genotype and allele distributions of ACTN3 R577X polymorphism in Turkish professional hip- hop and latin dancers and compared them to non-dancers as a control group. 30 professional dancers and non-dancers were recruited for the study. A genotyping procedure was carried out by a newly introduced four-primer PCR methodology. For statistical analysis, the Chi-square test was used to compare data between the groups (p<0,05 evaluated as significant). Numbers and the percentages of dancers were 2 (7%), 21 (70%) and 7(23%) for RR, RX and XX genotypes, respectively. The same numbers and the percentages were 15 (50%), 8 (15%) and 7 (23%) for RR, RX and XX genotypes, respectively, for the controls.
    [Show full text]
  • Troponin Variants in Congenital Myopathies: How They Affect Skeletal Muscle Mechanics
    International Journal of Molecular Sciences Review Troponin Variants in Congenital Myopathies: How They Affect Skeletal Muscle Mechanics Martijn van de Locht , Tamara C. Borsboom, Josine M. Winter and Coen A. C. Ottenheijm * Department of Physiology, Amsterdam Cardiovascular Sciences, Amsterdam UMC, Location VUmc, 1081 HZ Amsterdam, The Netherlands; [email protected] (M.v.d.L.); [email protected] (T.C.B.); [email protected] (J.M.W.) * Correspondence: [email protected]; Tel.: +31-(0)-20-444-8123 Abstract: The troponin complex is a key regulator of muscle contraction. Multiple variants in skeletal troponin encoding genes result in congenital myopathies. TNNC2 has been implicated in a novel congenital myopathy, TNNI2 and TNNT3 in distal arthrogryposis (DA), and TNNT1 and TNNT3 in nemaline myopathy (NEM). Variants in skeletal troponin encoding genes compromise sarcomere function, e.g., by altering the Ca2+ sensitivity of force or by inducing atrophy. Several potential therapeutic strategies are available to counter the effects of variants, such as troponin activators, introduction of wild-type protein through AAV gene therapy, and myosin modulation to improve muscle contraction. The mechanisms underlying the pathophysiological effects of the variants in skeletal troponin encoding genes are incompletely understood. Furthermore, limited knowledge is available on the structure of skeletal troponin. This review focusses on the physiology of slow and fast skeletal troponin and the pathophysiology of reported variants in skeletal troponin encoding genes. A better understanding of the pathophysiological effects of these variants, together with enhanced knowledge regarding the structure of slow and fast skeletal troponin, will direct the development of Citation: van de Locht, M.; treatment strategies.
    [Show full text]
  • Α-Actinin/Titin Interaction: a Dynamic and Mechanically Stable Cluster of Bonds in the Muscle Z-Disk
    α-Actinin/titin interaction: A dynamic and mechanically stable cluster of bonds in the muscle Z-disk Marco Grisona, Ulrich Merkela, Julius Kostanb, Kristina Djinovic-Carugob,c, and Matthias Riefa,d,1 aPhysik Department E22, Technische Universität München, 85748 Garching, Germany; bDepartment of Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, A-1030 Vienna, Austria; cDepartment of Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia; and dMunich Center for Integrated Protein Science, 81377 Munich, Germany Edited by James A. Spudich, Stanford University School of Medicine, Stanford, CA, and approved December 16, 2016 (received for review August 2, 2016) Stable anchoring of titin within the muscle Z-disk is essential for In humans, the isoforms of titin exhibit four to seven Z-repeats preserving muscle integrity during passive stretching. One of the (15, 16, 20). The structure of the EF3-4 hands complex with titin main candidates for anchoring titin in the Z-disk is the actin cross- Z-repeat 7 shows the bound Z-repeat in an α-helical confor- linker α-actinin. The calmodulin-like domain of α-actinin binds to mation (21). In solution assays, binding affinities of various the Z-repeats of titin. However, the mechanical and kinetic prop- Z-repeats to EF3-4 were determined to lie in the micromolar erties of this important interaction are still unknown. Here, we use range (22). Micromolar affinity points only to a moderately a dual-beam optical tweezers assay to study the mechanics of this stable interaction, the kinetics of which are unknown.
    [Show full text]
  • Current Understanding of the Role of Cytoskeletal Cross-Linkers in the Onset and Development of Cardiomyopathies
    International Journal of Molecular Sciences Review Current Understanding of the Role of Cytoskeletal Cross-Linkers in the Onset and Development of Cardiomyopathies Ilaria Pecorari 1, Luisa Mestroni 2 and Orfeo Sbaizero 1,* 1 Department of Engineering and Architecture, University of Trieste, 34127 Trieste, Italy; [email protected] 2 University of Colorado Cardiovascular Institute, University of Colorado Anschutz Medical Campus, Aurora, CO 80045, USA; [email protected] * Correspondence: [email protected]; Tel.: +39-040-5583770 Received: 15 July 2020; Accepted: 10 August 2020; Published: 15 August 2020 Abstract: Cardiomyopathies affect individuals worldwide, without regard to age, sex and ethnicity and are associated with significant morbidity and mortality. Inherited cardiomyopathies account for a relevant part of these conditions. Although progresses have been made over the years, early diagnosis and curative therapies are still challenging. Understanding the events occurring in normal and diseased cardiac cells is crucial, as they are important determinants of overall heart function. Besides chemical and molecular events, there are also structural and mechanical phenomena that require to be investigated. Cell structure and mechanics largely depend from the cytoskeleton, which is composed by filamentous proteins that can be cross-linked via accessory proteins. Alpha-actinin 2 (ACTN2), filamin C (FLNC) and dystrophin are three major actin cross-linkers that extensively contribute to the regulation of cell structure and mechanics. Hereby, we review the current understanding of the roles played by ACTN2, FLNC and dystrophin in the onset and progress of inherited cardiomyopathies. With our work, we aim to set the stage for new approaches to study the cardiomyopathies, which might reveal new therapeutic targets and broaden the panel of genes to be screened.
    [Show full text]
  • Titin N2A Domain and Its Interactions at the Sarcomere
    International Journal of Molecular Sciences Review Titin N2A Domain and Its Interactions at the Sarcomere Adeleye O. Adewale and Young-Hoon Ahn * Department of Chemistry, Wayne State University, Detroit, MI 48202, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-(313)-577-1384 Abstract: Titin is a giant protein in the sarcomere that plays an essential role in muscle contraction with actin and myosin filaments. However, its utility goes beyond mechanical functions, extending to versatile and complex roles in sarcomere organization and maintenance, passive force, mechanosens- ing, and signaling. Titin’s multiple functions are in part attributed to its large size and modular structures that interact with a myriad of protein partners. Among titin’s domains, the N2A element is one of titin’s unique segments that contributes to titin’s functions in compliance, contraction, structural stability, and signaling via protein–protein interactions with actin filament, chaperones, stress-sensing proteins, and proteases. Considering the significance of N2A, this review highlights structural conformations of N2A, its predisposition for protein–protein interactions, and its multiple interacting protein partners that allow the modulation of titin’s biological effects. Lastly, the nature of N2A for interactions with chaperones and proteases is included, presenting it as an important node that impacts titin’s structural and functional integrity. Keywords: titin; N2A domain; protein–protein interaction 1. Introduction Citation: Adewale, A.O.; Ahn, Y.-H. The complexity of striated muscle is defined by the intricate organization of its com- Titin N2A Domain and Its ponents [1]. The involuntary cardiac and voluntary skeletal muscles are the primary types Interactions at the Sarcomere.
    [Show full text]
  • Alpha-Actinin Binding Kinetics Modulate Cellular Dynamics And
    Alpha-actinin binding kinetics modulate cellular SEE COMMENTARY dynamics and force generation Allen J. Ehrlichera,b,c,1, Ramaswamy Krishnand, Ming Guob, Cécile M. Bidand, David A. Weitzb, and Martin R. Pollaka,1 aDivision of Nephrology, Department of Medicine, and dDepartment of Emergency Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215; bSchool of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138; and cDepartment of Bioengineering, McGill University, Montreal, QC, Canada H3A0C3 Contributed by Martin R. Pollak, March 25, 2015 (sent for review January 14, 2015) The actin cytoskeleton is a key element of cell structure and homology regions, which together create actin-binding domains movement whose properties are determined by a host of accessory (ABDs). These domains on opposite ends of the dimer allow proteins. Actin cross-linking proteins create a connected network α-actinin to act as a cross-linker, forming networks of loose from individual actin filaments, and though the mechanical effects bundles of actin filaments (11, 12). In humans, there are four of cross-linker binding affinity on actin networks have been in- genes that encode highly homologous forms of α-actinin. Point vestigated in reconstituted systems, their impact on cellular forces is mutations in the ABD of ACTN4 cause a form of kidney damage unknown. Here we show that the binding affinity of the actin cross- known as focal segmental glomerulosclerosis (FSGS) (13–15). linker α-actinin 4 (ACTN4) in cells modulates cytoplasmic mobility, With FSGS, the specialized podocyte cells that form part of the cellular movement, and traction forces. Using fluorescence recovery filtration barrier between the blood and urine lose their normal after photobleaching, we show that an ACTN4 mutation that causes extended structure (13).
    [Show full text]
  • Actin-Titin Interaction in Cardiac Myofibrils: Probing a Physiological Role
    Biophysical Journal Volume 73 August 1997 905-919 905 Actin-Titin Interaction in Cardiac Myofibrils: Probing a Physiological Role Wolfgang A. Linke,* Marc lvemeyer,* Siegfried Labeit,# Horst Hinssen,§ J. Caspar Ruegg,* and Mathias Gautel# *Institute of Physiology II, University of Heidelberg, D-69120 Heidelberg; #European Molecular Biology Laboratory, D-69012 Heidelberg; and §Biochemical Cell Biology Group, University of Bielefeld, D-33501 Bielefeld, Germany ABSTRACT The high stiffness of relaxed cardiac myofibrils is explainable mainly by the expression of a short-length titin (connectin), the giant elastic protein of the vertebrate myofibrillar cytoskeleton. However, additional molecular features could account for this high stiffness, such as interaction between titin and actin, which has previously been reported in vitro. To probe this finding for a possible physiological significance, isolated myofibrils from rat heart were subjected to selective removal of actin filaments by a calcium-independent gelsolin fragment, and the "passive" stiffness of the specimens was recorded. Upon actin extraction, stiffness decreased by nearly 60%, and to a similar degree after high-salt extraction of thick filaments. Thus actin-titin association indeed contributes to the stiffness of resting cardiac muscle. To identify possible sites of association, we employed a combination of different techniques. Immunofluorescence microscopy revealed that actin extraction increased the extensibility of the previously stiff Z-disc-flanking titin region. Actin-titin interaction within this region was confirmed in in vitro cosedimentation assays, in which multimodule recombinant titin fragments were tested for their ability to interact with F-actin. By contrast, such assays showed no actin-titin-binding propensity for sarcomeric regions outside the Z-disc comb.
    [Show full text]
  • 6. Muscle Contraction
    Muscle contraction ANSC (FSTC) 607 Physiology and Biochemistry of Muscle as a Food MUSCLE CONTRACTION I. Basic model of muscle contraction A. Overall 1. Calcium is released from sarcoplasmic reticulum. 2. Myosin globular head (S1) interacts with F-actin. 3. Thick and thin filaments slide past each other. 4. Calcium is resequestered in sarcoplasmic reticulum. 5. Muscle relaxes. B. Role of ATP 1. Charges myosin heads by forming charged myosin-ATP intermediate (actually myosin-ADP•Pi). 2. Provides energy for power stroke, which allows for release of myosin head from actin (i.e., breaks the rigor bond). CHEMICAL EVENTS of the muscle-contraction cycle are outlined as they take place in the soluble experimental system described by the authors. A myosin head combines with a molecule of adenosine triphosphate (ATP). The myosin-ATP is somehow raised to a “charged” intermediate form that binds to an actin molecule of the thin filament. The combination, the “active complex,” undergoes hydrolysis: the ATP splits into adenosine diphosphate (ADP) and inorganic phosphate and energy is released (which in intact muscle powers contraction). The resulting “rigor complex” persists until a new ATP molecule binds to the myosin head; the myosin-ATP is recycled, recharged and once again undergoes hydrolysis. 1 Muscle contraction II. Cooperative action of muscle proteins A. Requirement for troponin/tropomyosin 1. ATPase in intact thin filaments plus myosin heads requires calcium for binding. 2. Purified actin plus myosin heads S1 have high ATPase activity even in the absence of calcium, so that F-actin will bind to a charged myosin head (M-ADP-Pi) in the absence of calcium.
    [Show full text]
  • Modeling the Response of Troponin C to Calcium in Increasingly Complex Systems
    Modeling the response of troponin C to calcium in increasingly complex systems DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jalal Khalid Siddiqui Graduate Program in Biophysics The Ohio State University 2016 Dissertation Committee: Dr. Jonathan Davis, Adviser Dr. Brandon Biesiadecki Dr. Mark Ziolo Dr. Thomas Hund Copyright by Jalal Khalid Siddiqui 2016 Abstract Troponin C (TnC) is a calcium-sensing switch that regulates contraction and relaxation in skeletal and cardiac muscle. Mutations in troponin (TnC, troponin I (TnI), troponin T (TnT)) that alter the apparent Ca2+ binding properties of TnC have been implicated in several cases of cardiomyopathy. Further studies have focused on TnC as a target for pharmacological intervention, and a recently engineered Ca2+-sensitized TnC variant has been shown to enhance contractility in mice with myocardial infarction. Previous studies have shown that the Ca2+ binding properties of TnC depend not only on troponin interactions but also upon interactions of many other myofilament proteins. Furthermore, many of these proteins are targets for phosphorylation and other post-translational modifications that alter the apparent Ca2+ binding properties of TnC. In this regard, TnC is not merely a simple switch, but a central hub receiving input from several other proteins. Studies have shown that while isolated TnC has a low Ca2+ binding affinity, the Tn complex has a high Ca2+ binding affinity. Thin filaments containing the Tn complex and actin/tropomyosin have an intermediate affinity which is restored to high affinity similar to that of the Tn complex by the addition of S1 myosin.
    [Show full text]
  • IL-33 Activates Tumor Stroma to Promote Intestinal Polyposis
    IL-33 activates tumor stroma to promote PNAS PLUS intestinal polyposis Rebecca L. Maywalda, Stephanie K. Doernerb, Luca Pastorellic,d,e, Carlo De Salvoc, Susan M. Bentona, Emily P. Dawsona, Denise G. Lanzaa, Nathan A. Bergerb,f,g,h, Sanford D. Markowitzh,i,j, Heinz-Josef Lenzk, Joseph H. Nadeaul, Theresa T. Pizarroc, and Jason D. Heaneya,m,n,1 aDepartment of Molecular and Human Genetics, mDan L. Duncan Cancer Center, and nTexas Medical Center Digestive Diseases Center, Baylor College of Medicine, Houston, TX 77030; Departments of bGenetics and Genome Sciences, cPathology, fBiochemistry, and iMedicine, gCenter for Science, Health and Society, hCase Comprehensive Cancer Center, and jUniversity Hospitals Case Medical Center, Case Western Reserve University School of Medicine, Cleveland, OH 44106; dDepartment of Biomedical Sciences for Health, University of Milan, Milan 20133, Italy; eGastroenterology and Gastrointestinal Endoscopy Unit, Istituto di Ricovero e Cura a Carattere Scientifico Policlinico San Donato, San Donato Milanese 20097, Italy; lPacific Northwest Research Institute, Seattle, WA 98122; and kDivision of Medical Oncology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033 Edited by Charles A. Dinarello, University of Colorado Denver, Aurora, CO, and approved April 2, 2015 (received for review November 25, 2014) Tumor epithelial cells develop within a microenvironment consist- epithelial restitution and proliferation (6, 7). The CRC stroma ing of extracellular matrix, growth factors, and cytokines produced acquires a similar activated phenotype and produces the same by nonepithelial stromal cells. In response to paracrine signals from soluble factors and ECM components associated with inflammation tumor epithelia, stromal cells modify the microenvironment to pro- and wound healing to promote proliferation and survival of trans- mote tumor growth and metastasis.
    [Show full text]