Isolation, characterization and N-terminal sequences of the CNBr-cleavage peptides from human complement Factor B. Localization of a free thiol group and a sequence defining the site cleaved by factor D.
Nine CNBr-cleavage peptides from Factor B (a component of the alternative pathway of complement) were isolated. Each was characterized by amino acid analysis and automated Edman degradation. One peptide contained a methionyl bond resistant to cleavage by CNBr. The number of CNBr-cleavage peptides is in agreement with the results of amino acid analysis of Factor B and the fragments Ba and Bb. A total of 358 unique residues were identified from the N-terminal sequences of the CNBr-cleavage peptides. These represent approx. 50% and 60% of the total residues of Factor B and fragment Bb respectively. Alignment of two CNBr-cleavage peptides (CB-VIc and CB-IV) provided a continuous segment of 140 residues. This sequence contained the site cleaved by Factor D to generate the Ba and Bb fragments during the activation of complement. Peptide CB-IV contained a free thiol group at a position corresponding to residue 33 of fragment Bb. Amino sugar analyses of Factor B and of fragments Bb and Ba indicated that all the carbohydrate structures of factor B are N-linked to asparagine through N-acetylglucosamine. The two carbohydrate-attachment sites of the Bb fragment were identified.
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000606:Amino Sugars / Q000032:analysis; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003166:Complement Activating Enzymes; D003488:Cyanogen Bromide / Q000378:metabolism; D006801:Humans; D010446:Peptide Fragments / Q000032:analysis* / Q000302:isolation & purification; D013438:Sulfhydryl Compounds / Q000032:analysis
D000596:Amino Acids; D000606:Amino Sugars; D010446:Peptide Fragments; D013438:Sulfhydryl Compounds; D003166:Complement Activating Enzymes; D003488:Cyanogen Bromide