MARCH-XI, a novel transmembrane ubiquitin ligase implicated in ubiquitin-dependent protein sorting in developing spermatids.

A mechanism by which ubiquitinated cargo proteins are sorted into multivesicular bodies (MVBs) from plasma and trans-Golgi network (TGN) membranes is well established in yeast and mammalian somatic cells. However, the ubiquitin-dependent sorting pathway has not been clearly defined in germ cells. In this study we identified a novel member ...
of the transmembrane RING-finger family of proteins, termed membrane-associated RING-CH (MARCH)-XI, that is expressed predominantly in developing spermatids and weakly in brain and pituitary. MARCH-XI possesses an E3 ubiquitin ligase activity that targets CD4 for ubiquitination. Immunoelectron microscopy of rat round spermatids showed that MARCH-XI is localized to TGN-derived vesicles and MVBs. Fluorescence staining of rat round spermatids and immunoprecipitation of rat testis demonstrated that MARCH-XI forms complexes with the adaptor protein complex-1 and with fucose-containing glycoproteins including ubiquitinated forms. Furthermore, the C-terminal region of MARCH-XI mediates its interaction with mu1-adaptin and Veli through a tyrosine-based motif and a PDZ binding motif, respectively. Our data suggest that MARCH-XI acts as a ubiquitin ligase with a role in ubiquitin-mediated protein sorting in the TGN-MVB transport pathway, which may be involved in mammalian spermiogenesis.
Mesh Terms:
Amino Acid Motifs, Amino Acid Sequence, Animals, Brain, Cloning, Molecular, Male, Microscopy, Immunoelectron, Molecular Sequence Data, Pituitary Gland, Protein Binding, Rats, Recombinant Proteins, Spermatids, Ubiquitin, Ubiquitin-Protein Ligases
J. Biol. Chem.
Date: Aug. 24, 2007
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