The four-helix bundle of the neuronal target membrane SNARE complex is neither disordered in the middle nor uncoiled at the C-terminal region.
Assembly of the SNARE complex is an essential step for membrane fusion and neurotransmitter release in neurons. The plasma membrane SNAREs syntaxin 1A and SNAP-25 (t-SNAREs) and the delivery-vesicle SNARE VAMP2 (or v-SNARE) contain the "SNARE regions" that essentially mediate SNARE pairing. Using site-directed spin labeling and EPR distance measurement we show that two identical copies of the SNARE region from syntaxin 1A intertwine as a coiled coil near the "ionic layer" region. The structure of the t-SNARE complex appears to be virtually identical to that of the ternary SNARE complex, except that VAMP2 is substituted to the second copy of syntaxin 1A. Furthermore, it appears that the coiled coil structure is maintained up to residue 259 of syntaxin 1A, identical to that of the ternary complex. These results are somewhat contradictory to the previous reports, suggesting that the t-SNARE complex has the disordered midsection (Xiao, W. Z., Poirier, M. A., Bennett, M. K., and Shin, Y. K. (2001) Nat. Struc. Biol. 8, 308-311) and the uncoiled C-terminal region (Margittai, M., Fasshauer, D., Pabst, S., Jahn, R., and Langen, R. (2001) J. Biol. Chem. 276, 13169-13177). The newly refined structure of the t-SNARE complex provides a basis for the better understanding of the SNARE assembly process. It also provides possible structural-functional clues to the membrane fusion in the v-SNARE deleted fusion models.
Zhang
Fan
F
Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.
Chen
Yong
Y
Kweon
Dae-Hyuk
DH
Kim
Chang Sup
CS
Shin
Yeon-Kyun
YK
D000595:Amino Acid Sequence; D000818:Animals; D004578:Electron Spin Resonance Spectroscopy; D005982:Glutathione Transferase / Q000737:chemistry / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000737:chemistry; D009474:Neurons / Q000502:physiology*; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D050600:SNARE Proteins; D017384:Sequence Deletion; D033921:Vesicular Transport Proteins
D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D005982:Glutathione Transferase