Elucidation of the disulfide-bonding pattern in the factor I modules of the sixth component (C6) of human complement

• Published in: Biochimica et biophysica acta 1997-09, Vol.1342 (1), p.13-18
• Main Authors: Lengweiler, Stephan, Schaller, Johann, DiScipio, Richard G, Rickli, Egon E
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Binding Sites; Chromatography, High Pressure Liquid; Complement; Complement C6 - chemistry; Cysteine; Cystine; Disulfide bridge; Disulfides; Factor I; Fibrinogen - chemistry; Humans; Peptide Fragments - chemistry; Peptide Fragments - isolation & purification; Protein module; Subtilisins; Trypsin
• ISSN: 0167-4838; 0006-3002; 1879-2588
• DOI: 10.1016/S0167-4838(97)00072-1

Complement component C6 is known to contain two factor I modules in tandem at its C-terminus. To localize the disulfide bridges in those domains, native C6 was cleaved with trypsin, followed by subtilisin. The resulting digests were separated by reversed-phase HPLC, and all of the potential cystine-containing fragments were detected by a fluorescence assay and amino acid composition analyses. Final identification of the disulfide bonds was achieved by Edman degradation of the corresponding peptides. From the data gained a 1–3, 2–9, 4–7, 5–10, 6–8 pattern was determined (Cys 752–Cys 802, Cys 763–Cys 780, Cys 765–Cys 816, Cys 772–Cys 795, Cys 841–Cys 852, Cys 846–Cys 898, Cys 859–Cys 876, Cys 861–Cys 911, Cys 867–Cys 891). These findings are compared with the strongly related complement components C7 and factor I.