Longin <p>VAMPs (and its homologue synaptobrevins) define a group of SNARE proteins that contain a C-terminal coiled-coil/SNARE domain, in combination with variable N-terminal domains that are used to classify VAMPs: those containing longin N-terminal domains (~150 aa) are referred to as longins, while those with shorter N-termini are referred to as brevins [<cite idref="PUB00013945"/>]. Longins are the only type of VAMP protein found in all eukaryotes, suggesting that their longin domain is essential. The longin domain is thought to exert a regulatory function. Longin domains have been shown to share the same structural fold, a profilin-like globular domain consisting of a five-stranded antiparallel beta-sheet that is sandwiched by an alpha-helix on one side, and two alpha-helices on the other (beta(2)-alpha-beta(3)-alpha(2)).</p>