Ability of human SNAP-23 to generate high molecular weight SDS-resistant ternary SNARE complexes is influenced by C-terminal coil content

Using in vitro protein complex formation assay, ability of SNAP-25 isoforms to generate SDS-resistant ternary SNARE complexes with Syntaxin-1 and VAMP-2 was investigated. Major SNAP-25 family proteins were found to generate heat-resistant ternary complexes with varying efficiency. Compared to human SNAP-25, its non-neuronal counterparts SNAP-23 and SNAP-29 formed lower amounts of ternary complexes. Changing Pro182 in human SNAP-23 to Arg182 (SNAP-23 P182R) improved its ability to bind partners and form complexes. In silico analysis of C-terminal helical content in various SNAP-25 family members showed that except human SNAP-23, all others displayed secondary α-helical conformation. We also report that human SNAP-29 is resistant to the proteolytic action of botulinum neurotoxin A even when applied at large concentration.