Polymerization of factor B of the alternative complement pathway via disulfide bond(s) in the presence of Cu 2+ and stimulation by C3b, the major fragment of C3

Abstract

Factor B (B) of the alternative complement pathway has been found to dimerize via disulfide bond(s) in the presence of CuCl 2. Poly B has no B activity. The Bb fragment was also dimerized, indicating that one free sulfhydryl group on the Bb portion might be involved in polymerization. The Ba fragment was not dimerized. C3b, the major fragment of C3, has the capacity to stimulate polymerization of B. Incubation of C3b, B and factor D in the presence of Mg 2+ and Cu 2+ resulted in the formation of poly B and diminished cleavage of B. These results suggest that polymerization of B due to Cu 2+ might be partly responsible for the impairment of C3 convertase activity of the alternative pathway.