IDENTIFICATION OF THE DISULFIDE BONDS OF HUMAN-COMPLEMENT CLS

Cls, one of the three subcomponents of Cl, the first component of the complement system, is a complex serine protease. To determine the disulfide-bonding pattern, fragments of Cls were generated by cleavage with pepsin, thermolysin, or subtilisin. Disulfide bonds have been identified by several methods, for example, direct observation of the phenylthiohydantoin derivative of cystine during Edman degradation of isolated peptides and placement in the known cDNA sequence. All of the 26 half-cystines are linked in disulfide bonds occurring at positions 50-68, 120-132, 128-141, 143-156, 160-187, 219-236, 279-326, 306-339, 344-388, 371-406, 410-534, 580-603, and 613-644. All of the disulfide bonds of the earlier described substructures of Cls, the EGF-homologous part, the two SCR units, and the two domains typical for Cls and Clr are localized within these domains.