Identification and characterization of taxilin isoforms.

The syntaxin family is implicated in intracellular vesicle traffic. We have recently identified taxilin, a novel syntaxin-binding protein, which has a long coiled-coil region in its C-terminal half. A database search has revealed the presence of two other molecules having a long coiled-coil region homologous to that of taxilin in mammals. Then, we here attempted to isolate and characterize the two molecules. Both the two molecules stoichiometrically interacted with several syntaxin family members. Then, we renamed original taxilin alpha-taxilin and named the two molecules beta- and gamma-taxilins, respectively. Beta-taxilin was a human homologue of chicken MDP77. Gamma-taxilin was an uncharacterized protein and Northern blot analysis revealed that gamma-taxilin was ubiquitously expressed. Beta- and gamma-taxilins preferentially interacted with syntaxin-1a and -4, respectively. The taxilin family members mutually interacted with the syntaxin family members. These results indicate that there is the taxilin family composed of at least three members in mammals.