RING-CH finger, H2 subclass (C4HC3-type), found in membrane-associated RING finger protein MARCH4, MARCH9, and similar proteins
This subfamily includes the closely related MARCH4 and MARCH9, both belonging to the family of MARCH E3 ligases. They downregulate major histocompatibility complex-I (MHC-I). In the presence of MARCH4 or MARCH9, MHC-I can be ubiquitinated and rapidly internalized by endocytosis, whereas MHC-I molecules lacking lysines in their cytoplasmic tail are resistant to downregulation. 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. Both MARCH4 and MARCH9 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.
Comment:based on the structure of human MARCH8 with bound Zn2+ ions through its RING-CH finger
Comment:RING-CH finger (C4HC3-type)
Comment:A RING finger typically binds two zinc atoms, with its Cys and/or His side chains in a unique "cross-brace" arrangement.
Comment:The RING fingers found in MARCH proteins have an unusual arrangement of zinc-coordinating residues: The conserved helix complete with tryptophan at the C-terminal end is present but the cysteines and histidines are arranged in the sequence as C4HC3-type, rather than the typical C3H2C3-type in RING-H2 finger.
Jiyao W et al.(2023). "The conserved domain database in 2023.",