Primary structure of the A chain of human complement-classical-pathway enzyme C1r. N-terminal sequences and alignment of autolytic fragments and CNBr-cleavage peptides.
Activated human complement-classical-pathway enzyme C1r has previously been shown to undergo autolytic cleavages occurring in the A chain [Arlaud, Villiers, Chesne & Colomb (1980) Biochim. Biophys. Acta 616, 116-129]. Chemical analysis of the autolytic products confirms that the A chain undergoes two major cleavages, generating three fragments, which have now been isolated and characterized. The N-terminal alpha fragment (approx. 210 residues long) has a blocked N-terminus, as does the whole A chain, whereas N-terminal sequences of fragments beta and gamma (approx. 66 and 176 residues long respectively) do not, and their N-terminal sequences were determined. Fragments alpha, beta and gamma, which are not interconnected by disulphide bridges, are located in this order within C1r A chain. Fragment gamma is disulphide-linked to the B chain of C1r, which is C-terminal in the single polypeptide chain of precursor C1r. CNBr cleavage of C1r A chain yields seven major peptides, CN1b, CN4a, CN2a, CN1a, CN3, CN4b and CN2b, which were positioned in that order, on the basis of N-terminal sequences of the methionine-containing peptides generated from tryptic cleavage of the succinylated (3-carboxypropionylated) C1r A chain. About 60% of the sequence of C1r A chain (440-460 residues long) was determined, including the complete sequence of the C-terminal 95 residues. This region shows homology with the corresponding parts of plasminogen and chymotrypsinogen and, more surprisingly, with the alpha 1 chain of human haptoglobin 1-1, a serine proteinase homologue.
Gagnon
J
J
Arlaud
G J
GJ
D000596:Amino Acids / Q000032:analysis; D002850:Chromatography, Gel; D003166:Complement Activating Enzymes; D015923:Complement C1r; D003171:Complement Pathway, Classical; D003488:Cyanogen Bromide; D006801:Humans; D008715:Methionine / Q000032:analysis; D008956:Models, Chemical; D010446:Peptide Fragments / Q000032:analysis*; D014357:Trypsin
D000596:Amino Acids; D010446:Peptide Fragments; D008715:Methionine; D003166:Complement Activating Enzymes; D014357:Trypsin; D015923:Complement C1r; D003488:Cyanogen Bromide