Extension of RasMol to display surfaces, to handle CML/XML and other new features
Herbert Jacob Bernstein, Frances C. Bernstein · Acta Crystallographica Section A Foundations of Crystallography · 2002
Nerve terminals release neurotransmitters from vesicles into the synaptic cleft upon transient increases in intracellular Ca 2+ .This process requires the formation of trans SNARE complexes and is regulated by accessory proteins including nsec1 and COMPLEXIN (CPX).Here we present the crystal structure of neuronal squid Sec1 from squid, which was solved by MAD at 2.4 Å. S-Sec1 folds into a modular arch-shaped three-domain assembly.Comparison of structures of squid s-Sec1 from different crystal forms, and rat nsec1 bound to syntaxin-1a (Misura et al. (2000), Nature 404, 355-362) indicates potential conformational rearrangements in domain 1 and 3. A hinge region between domains 1 and 2 may be involved in binding/release of SYNTAXIN (SX), which may also affect the conformational flexibility of the helical hairpin of domain 3.The release of SX from nsec1 is thought to follow SNARE complex formation.Neuronal SNARE complexes then bind to CPX, which couples neurotransmission to an increase in intracellular calcium.The crystal structure of a squid core CPX/SNARE complex solved by molecular replacement at 2.95 Å resolution shows a helical segment of CPX that binds in anti-parallel fashion to the four-helix bundle of the core SNARE complex.CPX interacts at its C-terminus with SX and SYNAPTOBREVIN around the ionic zero layer of the SNARE complex.We propose that CPX is part of a multi-protein complex that regulates membrane fusion of docked vesicles at a late pre-fusion stage.