The Lipid Bilayer Is a Two-Dimensional Fluid the Aqueous Environment Inside and Outside a Cell Prevents Membrane Lipids From
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Bacterial Cell Membrane
BACTERIAL CELL MEMBRANE Dr. Rakesh Sharda Department of Veterinary Microbiology NDVSU College of Veterinary Sc. & A.H., MHOW CYTOPLASMIC MEMBRANE ➢The cytoplasmic membrane, also called a cell membrane or plasma membrane, is about 7 nanometers (nm; 1/1,000,000,000 m) thick. ➢It lies internal to the cell wall and encloses the cytoplasm of the bacterium. ➢It is the most dynamic structure of a prokaryotic cell. Structure of cell membrane ➢The structure of bacterial plasma membrane is that of unit membrane, i.e., a fluid phospholipid bilayer, composed of phospholipids (40%) and peripheral and integral proteins (60%) molecules. ➢The phospholipids of bacterial cell membranes do not contain sterols as in eukaryotes, but instead consist of saturated or monounsaturated fatty acids (rarely, polyunsaturated fatty acids). ➢Many bacteria contain sterol-like molecules called hopanoids. ➢The hopanoids most likely stabilize the bacterial cytoplasmic membrane. ➢The phospholipids are amphoteric molecules with a polar hydrophilic glycerol "head" attached via an ester bond to two non-polar hydrophobic fatty acid tails. ➢The phospholipid bilayer is arranged such that the polar ends of the molecules form the outermost and innermost surface of the membrane while the non-polar ends form the center of the membrane Fluid mosaic model ➢The plasma membrane contains proteins, sugars, and other lipids in addition to the phospholipids. ➢The model that describes the arrangement of these substances in lipid bilayer is called the fluid mosaic model ➢Dispersed within the bilayer are various structural and enzymatic proteins, which carry out most membrane functions. ➢Some membrane proteins are located and function on one side or another of the membrane (peripheral proteins). -
Spring 2013 Lecture 23
CHM333 LECTURES 23: 3/25/13 SPRING 2013 Professor Christine Hrycyna LIPIDS III EFFECT OF CHOLESTEROL ON MEMBRANES: - Bulky rigid molecule - Moderates fluidity of membranes – both increases and decreases o Cholesterol in membranes DECREASES fluidity because it is rigid o Prevents crystallization (making solid) of fatty acyl side chains by fitting between them. Disrupts close packing of fatty acyl chains. Therefore, INCREASED fluidity BIOLOGICAL MEMBRANES CONTAIN PROTEINS AS WELL AS LIPIDS: - Proteins are 20-80% of cell membrane - Rest is lipid or carbohydrate; supramolecular assembly of lipid, protein and carbohydrate - Proteins are also distributed asymmetrically - TWO classes of Membrane Proteins: o Integral Membrane Proteins o Peripheral Membrane Proteins 178 CHM333 LECTURES 23: 3/25/13 SPRING 2013 Professor Christine Hrycyna - INTEGRAL MEMBRANE PROTEINS o Located WITHIN the lipid bilayer o Usually span the bilayer one or more times – called transmembrane (TM) proteins o Hydrophobic amino acids interact with fatty acid chains in the hydrophobic core of the membrane o Can be removed from the membrane with detergents like SDS – need to disrupt the hydrophobic interactions § Membrane Disruption Animation: o http://www.youtube.com/watch?v=AHT37pvcjc0 o Function: § Transporters – moving molecules into or out of cells or cell membranes § Receptors – transmitting signals from outside of the cell to the inside - β Barrel Integral Membrane Proteins § Barrel-shaped membrane protein that is made up of antiparallel β-strands with hydrophilic (interior) and hydrophobic (facing lipid tails). § So far found only in outer membranes of Gram-negative bacteria, cell wall of Gram-positive bacteria, and outer membranes of mitochondria and chloroplasts. 179 CHM333 LECTURES 23: 3/25/13 SPRING 2013 Professor Christine Hrycyna - α-Helical Membrane Proteins - Can cross the membrane once or many times and have multiple transmembrane segments. -
Membrane Structure Overview Pathology > Cellular Biology & Genetics > Cellular Biology & Genetics
Membrane Structure Overview Pathology > Cellular Biology & Genetics > Cellular Biology & Genetics PLASMA MEMBRANE • Phospholipid bilayer: bilayer that comprises mostly phospholipids • Fluid mosaic: mosaic of proteins embedded within a fluid phospholipid bilayer • Selectively permeable: some substances move through passively, others use proteins for transport MEMBRANE COMPONENTS • Phospholipids • Proteins • Cholesterol • Carbohydrates PHOSPHOLIPIDS • Amphipathic: hydrophilic head and hydrophobic fatty acid tails • Form liposomes in aqueous environment • Weak hydrophobic interactions = membrane fluidity • Saturated phospholipids: maximize hydrogens in fatty acid tails, no kinks • Unsaturated phospholipids: double bond produces kink, increases fluidity CHOLESTEROL • Temperature buffer • Moderate temperature: decreases fluidity, lessens lateral movement • Low temperature: increases fluidity, prevents solidification PROTEINS • Includes transmembrane proteins that span the bilayer (other types exist) • Proteins provide about half the mass of the membrane CARBOHYDRATES • Glycoproteins: branched carbohydrates covalently bound to proteins • Glycolipids: carbohydrates covalently bound to lipids (extracellular only) 1 / 5 CLINICAL CORRELATION: Blood types • Carbohydrates on surface of red blood cells must be compatible between donor & recipient in blood transfusion FUNCTIONS OF THE CELL MEMBRANE • Cell communication • Import and export of molecules • Cell growth • Cell motility Eukaryotes have internal membranes within the cell, prokaryotes do not. -
Predicting Protein-Membrane Interfaces of Peripheral Membrane
bioRxiv preprint doi: https://doi.org/10.1101/2021.06.28.450157; this version posted June 29, 2021. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Predicting protein-membrane interfaces of pe- ripheral membrane proteins using ensemble machine learning Alexios Chatzigoulas1,2,* and Zoe Cournia1,* 1Biomedical Research Foundation, Academy of Athens, 4 Soranou Ephessiou, 11527 Athens, Greece, 2Depart- ment of Informatics and Telecommunications, National and Kapodistrian University of Athens, 15784 Athens, Greece *To whom correspondence should be addressed. Abstract Motivation: Abnormal protein-membrane attachment is involved in deregulated cellular pathways and in disease. Therefore, the possibility to modulate protein-membrane interactions represents a new promising therapeutic strategy for peripheral membrane proteins that have been considered so far undruggable. A major obstacle in this drug design strategy is that the membrane binding domains of peripheral membrane proteins are usually not known. The development of fast and efficient algorithms predicting the protein-membrane interface would shed light into the accessibility of membrane-protein interfaces by drug-like molecules. Results: Herein, we describe an ensemble machine learning methodology and algorithm for predicting membrane-penetrating residues. We utilize available experimental data in the literature for training 21 machine learning classifiers and a voting classifier. Evaluation of the ensemble classifier accuracy pro- duced a macro-averaged F1 score = 0.92 and an MCC = 0.84 for predicting correctly membrane-pen- etrating residues on unknown proteins of an independent test set. -
An Overview of Lipid Membrane Models for Biophysical Studies
biomimetics Review Mimicking the Mammalian Plasma Membrane: An Overview of Lipid Membrane Models for Biophysical Studies Alessandra Luchini 1 and Giuseppe Vitiello 2,3,* 1 Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark; [email protected] 2 Department of Chemical, Materials and Production Engineering, University of Naples Federico II, Piazzale Tecchio 80, 80125 Naples, Italy 3 CSGI-Center for Colloid and Surface Science, via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy * Correspondence: [email protected] Abstract: Cell membranes are very complex biological systems including a large variety of lipids and proteins. Therefore, they are difficult to extract and directly investigate with biophysical methods. For many decades, the characterization of simpler biomimetic lipid membranes, which contain only a few lipid species, provided important physico-chemical information on the most abundant lipid species in cell membranes. These studies described physical and chemical properties that are most likely similar to those of real cell membranes. Indeed, biomimetic lipid membranes can be easily prepared in the lab and are compatible with multiple biophysical techniques. Lipid phase transitions, the bilayer structure, the impact of cholesterol on the structure and dynamics of lipid bilayers, and the selective recognition of target lipids by proteins, peptides, and drugs are all examples of the detailed information about cell membranes obtained by the investigation of biomimetic lipid membranes. This review focuses specifically on the advances that were achieved during the last decade in the field of biomimetic lipid membranes mimicking the mammalian plasma membrane. In particular, we provide a description of the most common types of lipid membrane models used for biophysical characterization, i.e., lipid membranes in solution and on surfaces, as well as recent examples of their Citation: Luchini, A.; Vitiello, G. -
Membrane Proteins Are Associated with the Membrane of a Cell Or Particular Organelle and Are Generally More Problematic to Purify Than Water-Soluble Proteins
Strategies for the Purification of Membrane Proteins Sinéad Marian Smith Department of Clinical Medicine, School of Medicine, Trinity College Dublin, Ireland. Email: [email protected] Abstract Although membrane proteins account for approximately 30 % of the coding regions of all sequenced genomes and play crucial roles in many fundamental cell processes, there are relatively few membranes with known 3D structure. This is likely due to technical challenges associated with membrane protein extraction, solubilization and purification. Membrane proteins are classified based on the level of interaction with membrane lipid bilayers, with peripheral membrane proteins associating non- covalently with the membrane, and integral membrane proteins associating more strongly by means of hydrophobic interactions. Generally speaking, peripheral membrane proteins can be purified by milder techniques than integral membrane proteins, whose extraction require phospholipid bilayer disruption by detergents. Here, important criteria for strategies of membrane protein purification are addressed, with a focus on the initial stages of membrane protein solublilization, where problems are most frequently are encountered. Protocols are outlined for the successful extraction of peripheral membrane proteins, solubilization of integral membrane proteins, and detergent removal which is important not only for retaining native protein stability and biological functions, but also for the efficiency of downstream purification techniques. Key Words: peripheral membrane protein, integral membrane protein, detergent, protein purification, protein solubilization. 1. Introduction Membrane proteins are associated with the membrane of a cell or particular organelle and are generally more problematic to purify than water-soluble proteins. Membrane proteins represent approximately 30 % of the open-reading frames of an organism’s genome (1-4), and play crucial roles in basic cell functions including signal transduction, energy production, nutrient uptake and cell-cell communication. -
Membrane Fluidity and the Perception of Environmental Signals In
Progress in Lipid Research 42 (2003) 527–543 www.elsevier.com/locate/plipres Review Membrane fluidity and the perception of environmental signals in cyanobacteria and plants Koji Mikami, Norio Murata* Department of Regulation Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan Accepted 22 April 2003 Abstract Photosynthetic organisms, namely, plants and cyanobacteria, are directly exposed to changes in their environment and their survival depends on their ability to acclimate to such changes. Several lines of evi- dence suggest that temperature stress, such as unusually low or high temperatures, and osmotic stress might be perceived by plants and cyanobacteria via changes in the fluidity of their cell membranes. The availability of techniques for gene-targeted mutagenesis and gene transfer, as well as for the analysis of genomes and transcripts, has allowed us to examine and evaluate this hypothesis and its implications. In this review, we summarize recent studies of the regulation of gene expression by changes in the extent of unsaturation of fatty acids and membrane fluidity, and we present a discussion of the induction of gene expression by environmental stress and of sensors of environmental conditions and relationships between their activity and the fluidity of membranes in cyanobacteria and plants. # 2003 Elsevier Ltd. All rights reserved. Contents 1. Introduction .......................................................................................................................................................... -
The Structure of Biological Membranes
The Structure of Biological Membranes Func7ons of Cellular Membranes 1. Plasma membrane acts as a selecvely permeable barrier to the environment • Uptake of nutrients • Waste disposal • Maintains intracellular ionic milieau 2. Plasma membrane facilitates communicaon • With the environment • With other cells • Protein secreon 3. Intracellular membranes allow compartmentalizaon and separaon of different chemical reac7on pathways • Increased efficiency through proximity • Prevent fu8le cycling through separaon Composi7on of Animal Cell Membranes • Hydrated, proteinaceous lipid bilayers • By weight: 20% water, 80% solids • Solids: Lipid Protein ~90% Carbohydrate (~10%) • Phospholipids responsible for basic membrane bilayer structure and physical proper8es • Membranes are 2-dimensional fluids into which proteins are dissolved or embedded The Most Common Class of PhospholipiD is FormeD from a Gycerol-3-P Backbone SaturateD FaJy AciD •Palmitate and stearate most common •14-26 carbons •Even # of carbons UnsaturateD FaJy AciD Structure of PhosphoglyceriDes All Membrane LipiDs are Amphipathic Figure 10-2 Molecular Biology of the Cell (© Garland Science 2008) PhosphoglyceriDes are Classified by their Head Groups Phosphadylethanolamine Phosphadylcholine Phosphadylserine Phosphadylinositol Ether Bond at C1 PS and PI bear a net negave charge at neutral pH Sphingolipids are the SeconD Major Class of PhospholipiD in Animal Cells Sphingosine Ceramides contain sugar moies in ether linkage to sphingosine GlycolipiDs are AbunDant in Brain Cells Figure 10-18 Molecular -
Structural Basis of Sterol Recognition and Nonvesicular Transport by Lipid
Structural basis of sterol recognition and nonvesicular PNAS PLUS transport by lipid transfer proteins anchored at membrane contact sites Junsen Tonga, Mohammad Kawsar Manika, and Young Jun Ima,1 aCollege of Pharmacy, Chonnam National University, Bukgu, Gwangju, 61186, Republic of Korea Edited by David W. Russell, University of Texas Southwestern Medical Center, Dallas, TX, and approved December 18, 2017 (received for review November 11, 2017) Membrane contact sites (MCSs) in eukaryotic cells are hotspots for roidogenic acute regulatory protein-related lipid transfer), PITP lipid exchange, which is essential for many biological functions, (phosphatidylinositol/phosphatidylcholine transfer protein), Bet_v1 including regulation of membrane properties and protein trafficking. (major pollen allergen from birch Betula verrucosa), PRELI (pro- Lipid transfer proteins anchored at membrane contact sites (LAMs) teins of relevant evolutionary and lymphoid interest), and LAMs contain sterol-specific lipid transfer domains [StARkin domain (SD)] (LTPs anchored at membrane contact sites) (9). and multiple targeting modules to specific membrane organelles. Membrane contact sites (MCSs) are closely apposed regions in Elucidating the structural mechanisms of targeting and ligand which two organellar membranes are in close proximity, typically recognition by LAMs is important for understanding the interorga- within a distance of 30 nm (7). The ER, a major site of lipid bio- nelle communication and exchange at MCSs. Here, we determined synthesis, makes contact with almost all types of subcellular or- the crystal structures of the yeast Lam6 pleckstrin homology (PH)-like ganelles (10). Oxysterol-binding proteins, which are conserved domain and the SDs of Lam2 and Lam4 in the apo form and in from yeast to humans, are suggested to have a role in the di- complex with ergosterol. -
The Membrane
The Membrane Natalie Gugala1*, Stephana J Cherak1 and Raymond J Turner1 1Department of Biological Sciences, University of Calgary, Canada *Corresponding author: RJ Turner, Department of Biological Sciences, University of Calgary, Alberta, Canada, Tel: 1-403-220-4308; Fax: 1-403-289-9311; Email: [email protected] Published Date: February 10, 2016 ABSTRACT and continues to be studied. The biological membrane is comprised of numerous amphiphilic The characterization of the cell membrane has significantly extended over the past century lipids, sterols, proteins, carbohydrates, ions and water molecules that result in two asymmetric polar leaflets, in which the interior is hydrophobic due to the hydrocarbon tails of the lipids. generated a dynamic heterogonous image of the membrane that includes lateral domains and The extension of the Fluid Mosaic Model, first proposed by Singer and Nicolson in 1972, has clusters perpetrated by lipid-lipid, protein-lipid and protein-protein interactions. Proteins found within the membrane, which are generally characterized as either intrinsic or extrinsic, have an array of biological functions vital for cell activity. The primary role of the membrane, among many, is to provide a barrier that conveys both separation and protection, thus maintaining the integrity of the cell. However, depending on the permeability of the membrane several ions are able to move down their concentration gradients. In turn this generates a membrane potential difference between the cytosol, which is found to have an excess negative charge, and surrounding extracellular fluid. Across a biological cell membrane, several potentials can be found. These include the Nernst or equilibrium potential, in which there is no overall flow of a Basicparticular Biochemistry ion and | www.austinpublishinggroup.com/ebooks the Donnan potential, created by an unequal distribution of ions. -
Biological Membranes
14 Biological Membranes To understand the structure The fundamental unit of life is the cell. All living things are composed of Goal and composition of biological cells, be it a single cell in the case of many microorganisms or a highly membranes. organized ensemble of myriad cell types in the case of multicellular organisms. A defining feature of the cell is a membrane, the cytoplasmic Objectives membrane, that surrounds the cell and separates the inside of the cell, the After this chapter, you should be able to cytoplasm, from other cells and the extracellular milieu. Membranes also • distinguish between cis and trans surround specialized compartments inside of cells known as organelles. unsaturated fatty acids. Whereas cells are typically several microns (μm) in diameter (although • explain why phospholipids some cells can be much larger), the membrane is only about 10 nanometers spontaneously form lipid bilayers and (nm) thick. Yet, and as we will see in subsequent chapters, the membrane is sealed compartments. not simply an ultra-thin, pliable sheet that encases the cytoplasm. Rather, • describe membrane fluidity and how it membranes are dynamic structures that mediate many functions in the is affected by membrane composition life of the cell. In this chapter we examine the composition of membranes, and temperature. their assembly, the forces that stabilize them, and the chemical and physical • explain the role of cholesterol in properties that influence their function. buffering membrane fluidity. The preceding chapters have focused on two kinds of biological molecules, • explain how the polar backbone namely proteins and nucleic acids, that are important in the workings of a membrane protein can be accommodated in a bilayer. -
Structural Evolution and Differential Effects on Lipid Bilayers
Biophysical Journal Volume 82 March 2002 1429–1444 1429 From Lanosterol to Cholesterol: Structural Evolution and Differential Effects on Lipid Bilayers Ling Miao,* Morten Nielsen,†‡ Jenifer Thewalt,§ John H. Ipsen,† Myer Bloom,¶ Martin J. Zuckermann,§‡ and Ole G. Mouritsen* *MEMPHYS, Physics Department, University of Southern Denmark-Odense, DK-5230 Odense M, Denmark; †Department of Chemistry, Technical University of Denmark, Building 206, DK-2800 Lyngby, Denmark; ‡Centre for the Physics of Materials, Department of Physics, McGill University, Montreal, Quebec H3A 2T5, Canada; §Department of Physics, Simon Fraser University, Burnaby, V5A 1S6 British Columbia, Canada; and ¶Department of Physics and Astronomy, University of British Columbia, Vancouver, V6T 1Z3 British Columbia, Canada ABSTRACT Cholesterol is an important molecular component of the plasma membranes of mammalian cells. Its precursor in the sterol biosynthetic pathway, lanosterol, has been argued by Konrad Bloch (Bloch, K. 1965. Science. 150:19–28; 1983. CRC Crit. Rev. Biochem. 14:47–92; 1994. Blonds in Venetian Paintings, the Nine-Banded Armadillo, and Other Essays in Biochemistry. Yale University Press, New Haven, CT.) to also be a precursor in the molecular evolution of cholesterol. We present a comparative study of the effects of cholesterol and lanosterol on molecular conformational order and phase equilibria of lipid-bilayer membranes. By using deuterium NMR spectroscopy on multilamellar lipid-sterol systems in combination with Monte Carlo simulations of microscopic models of lipid-sterol interactions, we demonstrate that the evolution in the molecular chemistry from lanosterol to cholesterol is manifested in the model lipid-sterol membranes by an increase in the ability of the sterols to promote and stabilize a particular membrane phase, the liquid-ordered phase, and to induce collective order in the acyl-chain conformations of lipid molecules.