Lysine residues, but not carbohydrates, are required for the regulatory function of H on the amplification C3 convertase of complement.
Lysine epsilon-amino groups of human factor H were selectively converted to guanidino groups by treatment with 0.1 M O-methylisourea at pH 10.4. Guanidination resulted in a dose-dependent decrease in the capacity of the regulatory protein to accelerate decay dissociation of P-stabilized amplification C3 convertase sites, to serve as a co-factor for cleavage of cell-bound C3b by I, and to compete for binding of 125I-untreated H to C3b. Modification of approximately 75% lysine epsilon-amino groups suppressed 97% of H functional activity. Biochemical analysis of native H demonstrated a total carbohydrate content of 18.5% (w/w) and the presence in the molecule of 11 biantennary oligosaccharidic chains of the N-acetyl-lactosaminic type. Total desialation of H by using Clostridium perfringens neuraminidase, and total deglycosylation of desialated H by using beta-endo-N-acetylglucosaminidase resulted in a 1.5- to 2-fold increase in H activity on a weight basis. Deglycosylation did not alter the capacity of H to discriminate between activating and nonactivating surfaces of the alternative pathway. Thus, lysine residues are important determinants of the binding capacity of H for cell-bound C3b, whereas the carbohydrate portion of the molecule is not required for the regulatory function of the protein on the amplification C3 convertase.
D000117:Acetylglucosamine / Q000378:metabolism; D050260:Carbohydrate Metabolism; D003166:Complement Activating Enzymes / Q000378:metabolism*; D050577:Complement C3-C5 Convertases / Q000378:metabolism*; D003179:Complement C3b / Q000378:metabolism; D003180:Complement C3b Inactivator Proteins / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D017242:Complement Factor H; D005690:Galactose / Q000378:metabolism; D006801:Humans; D008239:Lysine / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism; D008782:Methylurea Compounds / Q000494:pharmacology; D019158:N-Acetylneuraminic Acid; D009439:Neuraminidase / Q000494:pharmacology; D011485:Protein Binding; D012794:Sialic Acids / Q000378:metabolism
C493495:CFH protein, human; D003180:Complement C3b Inactivator Proteins; D008782:Methylurea Compounds; D012794:Sialic Acids; C002249:O-methylisourea; D003179:Complement C3b; D017242:Complement Factor H; D003166:Complement Activating Enzymes; D009439:Neuraminidase; D050577:Complement C3-C5 Convertases; D019158:N-Acetylneuraminic Acid; D008239:Lysine; D008358:Mannose; D000117:Acetylglucosamine; D005690:Galactose