Properdin is a gamma globulinprotein composed of multiple identical protein subunits with a separate ligand-binding site. Native properdin occurs in head-to-tail dimers, trimers and tetramers in the fixed ratio 22:52:28.[5]
The properdin promotes the association of C3b with Factor B and provides a focal point for the assembly of C3bBb on a surface. It binds to preformed alternative pathway C3-convertases.[6] Properdin also inhibits the Factor H – mediated cleavage of C3b by Factor I.
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Smith C, Pangburn M, Vogel CW, Müller-Eberhard H (1984). "Molecular Architecture of Human Properdin, a Positive Regulator of the Alternative Pathway of Complement". J Biol Chem. 259: R4582–4588.