Small Acidic Protein (SMAP)

SMAP1 and SMAP2 proteins constitute a subfamily of the Arf-specific GTPase-activating proteins. SMAP proteins bind to clathrin heavy chains and are involved in the trafficking of clathrin-coated vesicles. In cells, SMAP1 regulates Arf6-dependent endocytosis of transferrin receptors from the coated pits of the plasma membrane, whereas SMAP2 regulates Arf1-dependent retrograde transport of TGN38 from the early endosome to the trans-Golgi network. The common and distinct features of SMAP1 and SMAP2 activity provide a valuable opportunity to examine the differential regulation of membrane trafficking by these two proteins. In addition, a yeast two-hybrid system is described because of its utility in identifying novel molecules that interact with SMAP.