MAST205 is a testis-specific, cytoplasmic protein that functions in a multi-protein complex in the maturation of spermatids. MAST205 is involved in linking the dystrophin/utrophin network with microtubule filaments via Syntrophin. By forming a complex with TRAF6, MAST205 regulates lipopolysaccharide-induced IL-12 synthesis in macrophages. This leads to the inhibition of TRAF6 NF-B activation. Two isoforms exist for MAST205 due to alternative splicing. Isoform 1 represents the full length protein, while isoform 2 lacks the residues 327-396 and 1091-1113. The N-terminus of MAST205 must be phosphorylated in order for ubiquitination to occur at the same site. This ubiquitination leads to the degradation of MAST205 via proteasome-mediated proteolysis.