Identification and characterization of novel clathrin adaptor-related proteins

Abstract

We have identified a human ~87-kDa protein, designated as γ2-adaptin, that is similar to γ-adaptin (called γ1-adaptin in this paper), a large chain of the AP-1 clathrin-associated adaptor complex, not only in the primary structure (60% amino acid identity) but also in the domain organization. Northern blot analysis has shown that its mRNA is expressed in a variety of tissues. Analysis using a yeast two-hybrid system has revealed that, similarly to γ1-adaptin, γ2-adaptin is capable of interacting not only with the σ1 chain (called as σ1A in this paper), the small chain of the AP-1 complex, but also with a novel σ1-like protein, designated as σ1B, which shows an 87% amino acid identity to σ1a; and that, unlike γ1-adaptin, it is unable to interact with β1-adaptin, another large chain of the AP-1 complex. Immunofluorescence microscopy analysis has revealed that γ2- adaptin is localized to paranuclear vesicular structures that are not superimposed on structures containing γ1-adaptin. Furthermore, unlike γ1- adaptin, γ2-adaptin is recruited onto membranes in the presence of a fungal antibiotic, brefeldin A. These data suggest that γ2-adaptin constitute a novel adaptor-related complex that participates in a transport step different from that of AP-1.