Fig. 4. Aligned functional regions for syntaxins. This figure illustrates representative syntaxin homologs from evolutionarily diverse eukaryotes aligned in regions containing identified functional residues. (A) Region of the SNARE motif including the epimorphin region, which corresponds to positions 205-246 of R. norvegicus Syn1A. Aa shows the universally conserved Gln residue characteristic of syntaxins. Ab shows the identified Ile 236 residue from syntaxin 1A shown to be important for nSec1—syntaxin 1A complex formation. Ac and Ad underline the identified residues involved in Ca²⁺ channel interactions with syn1. (B) Botulism toxin binding region from syntaxin PM homologs, which corresponds to positions 162-170 of R. norvegicus Syn1A. Ba and Bb show the two residues also identified to be important for nSec1—syntaxin complex formation.