RING-CH finger, H2 subclass (C4HC3-type), found in membrane-associated RING finger protein MARCH4, MARCH9, MARCH11, and similar proteins
MARCH4 and MARCH9 are closely related to each other. They downregulate major histocompatibility complex-I (MHC-I). Moreover, MARCH4 and MARCH9, but not other MARCH proteins, can associate with Mult1 and prevent Mult1 expression at the cell surface in a lysine-dependent manner that can be reversed by heat shocking the cells. MARCH11 is a transmembrane RING-finger ubiquitin ligase that is predominantly expressed in developing spermatids in a stage-specific manner and is localized to the trans-Golgi network (TGN) vesicles and multivesicular bodies (MVBs). It mediates selective protein sorting via the TGN-MVB transport pathway through its ubiquitin ligase activity. SAMT family proteins have been identified as substrates of MARCH11 in mouse spermatids, suggesting that MARCH11 plays a role in mammalian spermiogenesis. Moreover, MARCH11 functions as an E3 ubiquitin ligase that targets CD4 for ubiquitination. It also forms complexes with the adaptor protein complex-1 and with fucose-containing glycoproteins including ubiquitinated forms. All family members contain an N-terminal C4HC3-type RING-CH finger, also known as vRING or RINGv, a variant of C3H2C3-type RING-H2 finger, followed by two transmembrane regions.