title: Structural homology of human complement component C8 gamma and plasma protein HC: identity of the cysteine bond pattern.
abstract: Anti-C8 alpha-gamma specific antibodies were used to isolate cDNA clones from a human liver expression library. Antibodies affinity-purified on the expressed hybrid protein of one clone bound exclusively to the gamma-chain of reduced C8 alpha-gamma. This clone, as well as a second full length cDNA clone obtained by hybridization screening, were sequenced and the complete primary structure for C8 gamma was established. Cyanogen bromide cleavage of C8 alpha-gamma released a 12 kDa carboxy-terminal C8 gamma fragment under both reducing and nonreducing conditions which was identified by fragment-specific, affinity-purified antibodies. Our data clearly show that C8 gamma has one internal disulfide bridge between cys-76 and cys-168 within the carboxy-terminal 12 kDa fragment, whereas the remaining cysteine residue 40 forms the disulfide bridge with C8 alpha. The overall sequence homology to plasma protein HC (23% amino acid identities) and the conservation of one internal cysteine bond and one free, surface-located cysteine residue suggests a highly conserved three-dimensional structure of C8 gamma and protein HC and also a possible functional relationship between these proteins.
mesh_terms: D000510:Alpha-Globulins / Q000032:analysis*; D000595:Amino Acid Sequence; D001483:Base Sequence; D003185:Complement C8 / Q000032:analysis* / Q000235:genetics; D003545:Cysteine; D004247:DNA / Q000032:analysis; D006801:Humans; D008969:Molecular Sequence Data
chemical_list: D000510:Alpha-Globulins; D003185:Complement C8; C016001:alpha-1-microglobulin; D004247:DNA; D003545:Cysteine