Tepsin associates with the adapter-like complex (AP-4) complex, which forms a non-clathrin coat around cytoplasmic vesicles in plants and animals []. Mutagenesis studies have identified two phylogenetically conserved peptide motifs within the C terminus of tepsin that interact with the C-terminal ear (or appendage) domains of the beta4 and epsilon subunits of AP-4 []. The homologue from Arabidopsis thaliana is known as MTV1 (At3g16270), which mediates clathrin-dependent trafficking of vacuolar cargo from the trans-Golgi network [].
Tepsin (also known as the product of the ENTHD2 or AP4AT gene) is an AP-4 accessory protein. It binds to the beta4-ear domain of AP-4, and is recruited to the trans-Golgi network (TGN) in manner dependent on this interaction []. This is the ENTH/VHS domain in tepsin and in A. thaliana protein At3g16270 [].Unlike the other members of the ENTH/ANTH/VHS superfamily, the tepsin ENTH domain lacks helix0, helix8, and a lipid binding pocket. Loss of helix0 precludes formation of a lipid binding pocket and explains why tepsin ENTH domain cannot interact directly with phosphoinositide head groups [].
