Acts as a cofactor for complement factor I, a serine protease which protects autologous cells against complement-mediated injury by cleaving C3b and C4b deposited on host tissue. May be involved in the fusion of the spermatozoa with the oocyte during fertilization. Also acts as a costimulatory factor for T-cells which induces the differentiation of CD4+ into T-regulatory 1 cells. T-regulatory 1 cells suppress immune responses by secreting interleukin-10, and therefore are thought to prevent autoimmunity. A number of viral and bacterial pathogens seem to exploit this property and directly induce an immunosuppressive phenotype in T-cells by binding to CD46.
Specificity
Natural and recombinant Human Membrane cofactor protein
Subcellular Location
Cytoplasmic vesicle secretory vesicle acrosome inner membrane Single-pass type I membrane protein Inner acrosomal membrane of spermatozoa. Internalized upon binding of Measles virus, Herpesvirus 6 or Neisseria gonorrhoeae, which results in an increased susceptibility of infected cells to complement-mediated injury. In cancer cells or cells infected by Neisseria, shedding leads to a soluble peptide.
Interacts with C3b and C4b. Binds to Measles virus H protein, to Human herpesvirus 6 GH protein and to human adenovirus B/D PIV/fiber protein, and acts as a receptor for these viruses. Binds to Streptococcus pyogenes M protein and to type IV pili from Neisseria, and may act as a receptor for these pathogenic bacteria.