Richard H. Scheller






		Richard H. Scheller Title Associate Investigator - HHMI Department Molecular and Cellular Physiology Research Interests Cellular and molecular analysis of neurotransmitter storage and release at the synapse. Email scheller@cmgm.stanford.edu Phone 723-9075 Fax 725-4436 Address Beckman Center B155 Mail Code: 5428 Faculty Research Description Mechanisms of Synaptic Transmission: When the action potential travels down the nerve and enters a release zone, changes in the membrane potential open channels which allow calcium to enter the cell. The calcium promotes transmitter release and membrane fusion. The membrane then recycles, forming new vesicles which are then replenished with chemical transmitter. This cycle might be considered the fundamental process that underlies nervous system function, yet little is known about the molecular mechanisms involved. In an attempt to define the molecular mechanisms which regulate membrane flow in the nerve, we have begun to characterize the proteins associated with the critical organelle in the process, the synaptic vesicle. Studies of these molecules have led to a working hypothesis for synaptic vesicle docking and fusion. We propose that the plasma membrane protein syntaxin is associated with a soluble factor, n-sec1, on the plasma membrane. As the vesicle docks, a 7S particle is formed as n-sec1 is displaced from the complex. The 7S particle is comprised of two vesicle-associated proteins, VAMP and synaptotagmin, and two components of the plasma membrane, SNAP-25 and syntaxin. At least part of the specificity of vesicle docking may be determined by interactions of the components of this 7S particle. Experiments in vitro demonstrated that as the soluble factor a-SNAP is added to the complex synaptotagmin is displaced. Only after a-SNAP is associated with the complex, can NSF bind forming an approximately 20S particle. Upon ATP hydrolysis by NSF, the particle dissociates leading to intermediates that precede the fusion of the lipid bilayers. The steps of this pathway, with the exception of those involving synaptotagmin, are proposed to occur in all vesicular docking and fusing reactions and are mediated by molecules which are members of gene families defined by the neural isoforms described above. We propose that in a nerve terminal the constitutive vesicle docking and fusion mechanism is used for synaptic transmission, however, a series of regulatory steps leading to the exquisite properties of the synapse are superimposed upon this machinery. One of the nervous system regulatory molecules may be synaptotagmin, however the mechanism of synaptotagmin action is not yet known. Many of the molecules discussed in the above model are structurally and functionally homologous to proteins which have been genetically identified in yeast to function in the secretory process. In yeast there are 14 genes which have been demonstrated to be required for the fusion of vesicles derived from the Golgi with the plasma membrane. Of these 15 genes only 7 have known homologues in mammalian systems. This suggests at least two possibilities. First, only a part of the pathway of secretion may be conserved from yeast to the mammalian nervous system or second, perhaps the homologous proteins have not yet been identified in mammals. In order to begin to differentiate between the two hypotheses, we have identified the first mammalian homologues of two of these yeast genes. The genes are homologues of the yeast proteins sec6 and sec8 and the rat homologues are referred to as rsec6 and rsec8. Both rsec6 and rsec8 are present in a 750 kDa complex comprised of 8 proteins. Amino acid sequencing of peptides derived from each of the bands reveals that each of the molecules are novel, previously undescribed proteins. peptide sequence information is being used to isolate the corresponding cDNA clones. The rsec6/8 complex is present in nerve terminals and is largely associated with the plasma membrane. Further biochemical and structural studies are aimed at understanding the specific roles of this large complex of proteins in secretion. Chao DS, Hay JC, Winnick S, Prekeris R, Klumperman J, Scheller RH. (1999). SNARE membrane trafficking dynamics in vivo. J Cell Biol 144:869-881. Chen YA, Scales SJ, Patel SM, Doung Y-C, Scheller RH. (1999). SNARE complex formation is triggered by Ca2+ and drives membrane fusion. Cell 97:165-174. Advani RJ, Yang B, Prekeris R, Lee KC, Klumperman J, Scheller RH. (1999). VAMP7 mediates vesicular transport from endosomes to lysosomes. J Cell Biol 146,4:765-775. Prekeris R, Foletti DL, Scheller RH. (1999). Dynamics of tubulo-vesicular recycling endosomes in hippocampal nuerons. J Neurosci 19,23:10324-10337. Misura KMS, Scheller RH, Weis WI. (In Press). Three dimensional structure of the neuronal-Sec1/syntaxin complex. Nature. Areas of Study Systems/Behavioral Neuroscience Cellular Neurobiology Molecular Neurobiology SBRC Ph.D.