Complement inhibition by human vitronectin involves non-heparin binding domains

Abstract

SUMMARYVitronectin (complement S-protein)., a multifunctional glycoprotein, inhibits complementmediated cytolysis at two identified stages of terminal complement complex (TCC) formation: blocking of C5b-7 membrane binding, and prevention of C9 polymerization. However, the functional domain(s) of vitronectin involved in these reactions remains incompletely defined. In order to identify the complement inhibition site, a 12-kD heparin binding fragment and two other internal fragments (53 kD and 43 kD) of vitronectin were isolated after cyanogen bromide (CNBr) treatment of the native molecule. Potent inhibition of guinea pig erythrocyte (GPE) reactive lysis was demonstrated with native vitronectin, total CNBr digest and the 53-kD and 43-kD fragments, but only very poorly by the heparin binding 12-kD peptide. Sitnilarly. the 43-kD fragment blocked the binding of C5b-7 to immobilized vitronectin. whereas the 12-kD fragment had no effect. These data localize the C5b-7 binding site to a 4.VkD internal region. Further characterization of the fragments was carried out in an assay which detected C9 polymerization in the presence of C5b-8. Polymerized material was separated by PAGE, detected by autoradiography and quantified after excision from the gels. Results showed that polymerization did not occur in the presence of the 53-kD and 43-kD fragments. However, the 12-kD heparin binding fragment had no effect. It is proposed that prevention of C5b-8-induced C9 polymerization resides at a site in an internal region of the vitronectin molecule.

Inhibition of the Membrane Attack Complex by Dengue Virus NS1 through Interaction with Vitronectin and Terminal Complement Proteins

“…5A). VN inhibited MAC formation, as expected (17). Interestingly, recombinant NS1 e also inhibited MAC activity, by 50%.…”

“…In addition, binding of C8 and C9 to the C5b7-VN complex leads to the formation of soluble C5b9 (SC5b9), which is hemolytically inactive. Furthermore, VN limits ongoing membrane-associated pore formation by inhibiting C9 polymerization (15)(16)(17). Acquisition of soluble human VN on the surfaces of microbial pathogens is a common complement evasion strategy that has been described for many bacterial pathogens (14,18); however, this particular evasion mechanism has never been evaluated in viral pathogens.…”

Molecular Aspects ofMoraxella catarrhalisPathogenesis

“…Though both UspA1 and UspA2 were found to be able to bind C3, a more dominant role was again observed for UspA2. Vitronectin is a regulatory component of the complement system that inhibits the terminal stages of the complement system by blocking membrane binding of C5b-7 and inhibition of C9 polymerization and eventually inhibiting formation of the MAC (97,134). UspA2 has been found to bind vitronectin (Fig.…”

Vitronectin in host pathogen interactions and antimicrobial therapeutic applications

“…Most of pathogenic bacteria bind to activated Vn, particularly either at the N-terminal polyanionic region (between amino acids 43-68) [9], the central domain containing hemopexin like domains (comprising residues 131-323) [38], or at the basic carboxy terminal HBD-3 [7]. The bacterial-Vn binding usually does not interfere with the Vn domain involved in the inhibition of C5b-9 complex (internal region between amino acid 51-310), thus allowing the complement regulator to remain active in inhibiting MAC formation while binding on the bacterial surface [30,39,40]. HBD-3 was proposed to be involved in the inhibition of the MAC [41].…”

“…HBD-3 was proposed to be involved in the inhibition of the MAC [41]. However, the inhibitory domain was later relocated as described above [39,40]. Interestingly, antimicrobial peptides (AMP) including LL37 and α-defensin share similar heparin binding motifs as seen in HBD-3 [42,43].…”