Article,

Regulators of complement activity mediate inhibitory mechanisms through a common C3b-binding mode.

, , , , , , , , , , , , , , and .
The EMBO journal, 35 (10): 1133--1149 (May 2016)
DOI: 10.15252/embj.201593673

Abstract

Regulators of complement activation (RCA) inhibit complement-induced immune responses on healthy host tissues. We present crystal structures of human RCA (MCP, DAF, and CR1) and a smallpox virus homolog (SPICE) bound to complement component C3b. Our structural data reveal that up to four consecutive homologous CCP domains (i-iv), responsible for inhibition, bind in the same orientation and extended arrangement at a shared binding platform on C3b. Large sequence variations in CCP domains explain the diverse C3b-binding patterns, with limited or no contribution of some individual domains, while all regulators show extensive contacts with C3b for the domains at the third site. A variation of~˜100° rotation around the longitudinal axis is observed for~domains binding at the fourth site on C3b, without affecting the overall binding mode. The data suggest a common evolutionary origin for both inhibitory mechanisms, called decay acceleration and cofactor activity, with variable C3b binding through domains at sites ii, iii, and iv, and provide a framework for understanding RCA disease-related mutations and immune evasion.

Tags

Users

  • @lambris

Comments and Reviews