12/27/01, 9:05 AM probably possesses an additional additional an possesses probably E. coli 4112 Simplified scheme of signal transduction in bacterial Observations made in our laboratory suggest that, in humans, humans, in that, laboratory suggest our Observations in made signal transduction pathway, different from the conventional conventional the from different pathway, transduction signal Currently we are tryingpathway. to understand two why by one and phosphorylation by (one activation signal of modes acetylation) are needed, to identify acetylation the roles of CheY and fumarate action, the and molecular to reveal mechanism pathway. signaling additional the underlying Mammalian chemotaxis the egg and sperm communicate prior to fertilization of way by chemotaxis. This process is mediated a chemoattractant(s) by when secreted from the egg or its surrounding cells and detected by responsiveness the sperm cells. demonstrated We that only a small fraction this of lose They the sperm population is chemotactically responsive given at any process. time, and that spermatozoa acquire this responsiveness as part of Fig. 1 Fig. of E. coli and S. typhimurium. Black stand arrows for regulated protein-protein interactions. is a response CheY regulator, CheA isa histidine kinase, and CheZ is a phosphatase. vivo occurs in also acetylation CheY that evidence provided and that, in the absence of Acs, chemotaxis is defective. (b) foundWe another component, fumarate, which modulates the probability of clockwise rotation. It does interacting so by with difference energy free standard the lowering and switch the between its clockwise and counterclockwise states. (c) We demonstrated that 972 8 934 Fax. 3923 [email protected] [email protected] 972 8 934 Tel. E-mail: Salmonella typhimurium typhimurium Salmonella Department of Biological Chemistry Department Chemotaxis: Chemotaxis: strategies Communication humans to from and 148 Escherichia coli A number of lines of evidence indicate that the signal We explore signalWe transduction strategiesusing chemotaxis transduction circuit, as currently known in chemotaxis in (Fig. known 1), currently as transduction circuit, is not complete. In a search for missing steps, we found a few additional players: (a) found We that phosphorylation is not the only chemical modification and not the only one of CheY that activates also the undergoes found protein. We that CheY specific acetylation at lysine residues, mediated the by enzyme acetyl-CoA synthetase (Acs), and that the consequence of this we Recently activity. CheY in increase large a is acetylation as a model. Bacterial chemotaxis is a sophisticated system system sophisticated chemotaxis a is Bacterial model. a as that integrates many different signals into a common output - a change in the direction of flagellar rotation. Our goal is to understand - a messenger protein how CheY that shuttles back and forth between the receptor supramolecular complex and the flagellar-motor supramolecular complex (Fig. - brings 1) about changes in the direction of flagellar rotation. found We that phosphorylation increases its binding of CheY to the switch protein FliM with a consequent increased probability of clockwise rotation, we identified the reciprocal binding domains on FliM and we further phosphorylation found that CheY alsoand CheY, regulatesthe termination of the signal controlling by the activity of a specific phosphatase, CheZ. Recently we investigated the correlation between the fraction of FliM molecules that are and theoccupied probability CheY by of clockwise rotation. We found that this probability increases only when most of the FliM and then the changemolecules is very are occupied CheY, by Furthermore,steep. the change in clockwise probability upon an increase in the occupancy of FliM level is not the inverse of the probability change upon a decrease in the occupancy, the function of the in hysteresis of involvement the suggesting switch within the flagellar-motor supramolecular complex.Such a situation of hysteresis, which involves a difference between the thresholds for clockwise rotation when the occupancy increases and decreases, might reflect a damping mechanism, which phosphorylation the in fluctuations which in situation a prevents throw the switch from of CheY level one direction of rotation to the other (Fig. 2). Signal transduction in bacterial chemotaxis bacterial in transduction Signal of the bacteria Rina Barak Anat Bren Ben-LuluGalit Cohen Sun Fei Jianshe Yan Yosef Yael Michael Eisenbach Michael

]148 michael_eizenbach michael_eizenbach Barak, R., Abouhamad, W. Abouhamad, R., Barak, Selected Publications in mammals. sperm chemotaxis of mechanism molecular the revealing towards step afirst as oviduct. We are the to chemoattractants currently identify trying rabbit’s the in found be can anegg atwhich window, time the with synchronized perfectly tobe found was state capacitated of the window time the and different, tobe found indeed was rabbit the in situation The by mating. induced rather but periodical not is ovulation where rabbit, the in stage capacitated sperm’s hypothesis to test by examining the timing and length of the with Recently, collaboration in ovulation. and the entry sperm between group oflinkage lack forthe tocompensate humans, in evolved was of which amechanism, is this that and mating, following cells L.C. ofcapacitated availability extended in results situation this that Giojalas wesuggested replaced, arecontinuously population a sperm within cells capacitated the that and vitro) in least (at 4 hours in Argentina, than more forno capacitated remain can cell sperm ahuman that observations our on Based terminated. is state capacitated the we put this Prasad, K., Caplan, S.R. and Eisenbach, M. (1998) (1998) M. Eisenbach, and S.R. Caplan, K., Prasad, ofthe Nterminus The (1998) M. Eisenbach, and A. Bren, Upper panel, direction of flagellar rotation. rotation. flagellar of direction panel, Upper CheY~P in levels. fluctuations random hypothetical Lower panel, rotation. (CCW) counterclockwise and (CW) CheY~P of clockwise for thresholds Fig. 2 the free energy difference between the clockwise and and clockwise the between difference energy free the Fumarate modulates bacterial flagellar rotation by lowering 507-514. CheY. regulator, response 278, Biol. J.Mol. chemotactic the for domain binding the is FliM, protein, switch flagellar 985-988. 180, J.Bacteriol. coli. inEscherichia rotation of flagellar are involved in acetate-stimulated change in the direction Asynthetase Coenzyme acetyl and kinase acetate Both Schematic presentation of the potential role of the different different the of role potential the of presentation Schematic 149 N. and Eisenbach, M. (1998) (1998) M. Eisenbach, and N. For additional information see: information For additional MINERVAthe Foundation. Chair in Biochemistry. Supported by grants from BSF, ISF, and Acknowledgements Bren, A. and Eisenbach, M. (2001) Changing the direction of direction the Changing (2001) M. Eisenbach, and A. Bren, ofthe Acetylation (2001) M. Eisenbach, and R. Barak, heard are signals How (2000) M. Eisenbach, and A. Bren, its and chemotaxis sperm Mammalian (1999) M. Eisenbach, 4, Rev. Reprod. chemotaxis. Sperm (1999) M. Eisenbach, eggs human Do (1999) Tur-Kaspa, M. and M. Eisenbach, and S. Tur-Kaspa, B.S., I., Dor,Jaiswal, J., Mashiach, Chemotactic-like (1999) M. Eisenbach, and R. Barak, Tur-Kaspa, I.(1999) and M. Eisenbach, B.S., Jaiswal, F.W. Dahlquist, A., Y., B., Bren, Blat, Eisenbach, and Gillespie, Eisenbach, Tur-Kaspa, I.and A., Cohen-Dayag, B.S., Jaiswal, www.weizmann.ac.il/Biological_Chemistry/scientist/Eisenbach Professorial Djanogly Simon and ofJack incumbent the is M.E. 312, 699-709. 312, Biol. J.Mol. FliM. protein switch ofthe states rotational the between ratio the bymodulating bacteria in rotation flagellar 731-743. 40, Microbiol. Mol. chemotaxis. CheY, regulator, response bacterial in involved is 182, 6865-6873. J.Bacteriol. propagation. signal sensory in interactions protein-protein chemotaxis: bacterial during 25,87-94. Dev. Genet. capacitation. with association 56-66. 21, BioEssays 203-210. spermatozoa? attract 1314-1319. Biol. 60, Reprod. progesterone a chemoattractant? is chemotaxis: sperm Human (1999) M. Eisenbach, Mol. Microbiol. 31, 1125-1137. overexpressed CheY. containing but machinery chemotaxis known the lacking cells coli ofEscherichia response 214-219. 5, Reprod. Hum. Mol. touse? probes and inducers which spermatozoa: human in reaction acrosome complete and ofpartial Detection 1191-1199. 284, Biol. J.Mol. chemotaxis. bacterial in activity ofphosphatase Regulation (1998) M. 427, 309-313. Lett. FEBS reaction. acrosome complete and partial both for aprerequisite all, after is, capacitation Sperm (1998) M. 821-828. states ofcounterclockwise the motor. J. Mol. Biol. 280,

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Cell Communication and Signal Transduction