SNARE-like superfamily

VAMPs (and its homologue synaptobrevins) define a group of SNARE proteins that contain a C-terminal coiled-coil/SNARE motif, 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 [12914952]. 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)).

Other families have been shown to contain domains that structurally resemble the VAMP longin domain. An example is the eukaryotic conserved protein, SEDL, which is a component of the transport protein particle (TRAPP), critically involved in endoplasmic reticulum-to-Golgi vesicle transport; mutations in the SEDL gene are associated with an X-linked skeletal disorder, spondyloepiphyseal dysplasia tarda [12361953]. Another example is the assembly domain of clathrin coat proteins, such as Mu2 adaptin (AP50) and Sigma2 adaptin (AP17), which structurally resemble the longin domain. AP50 and AP17 are two of the proteins that make up the core of AP2, a complex that functions in clathrin-mediated endocytosis [12086608].