Methionine modification impairs the C5-cleavage function of cobra venom factor-dependent C3/C5 convertase.
The complement-mediated lysis of guinea pig erythrocytes by cobra venom factor (CVF) decreased by 50-60% within 2 min of treatment with 5 mM sodium periodate at 0 degree C. This loss of activity paralleled modification of 3-4 Met; other amino acids and sugar residues of the oligosaccharide chains were not affected. Treatment with N-chlorosuccinimide or chloramine-T under conditions that specifically modified 3-4 readily-oxidizable Met also caused 50-60% loss of CVF activity. The secondary structure of CVF was not altered by these modifications. Methionine-modified CVF (MetCVF) supported the cleavage of factor B by factor D with equal efficiency as that of untreated CVF to form C3/C5 convertase (MetCVF,Bb) of the alternative pathway. MetCVF,Bb and CVF,Bb were indistinguishable with respect to C3 cleavage. However, the C5-cleavage ability of MetCVF,Bb was significantly lower than that of CVF,Bb. These results suggest the involvement of Met in CVF binding of C5.
Fu
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Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
McPhie
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P
Gowda
D C
DC
D000818:Animals; D003176:Complement C3 / Q000378:metabolism; D050577:Complement C3-C5 Convertases / Q000378:metabolism*; D003182:Complement C5 / Q000378:metabolism*; D011415:Complement Factor B / Q000187:drug effects / Q000378:metabolism; D004546:Elapid Venoms / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006168:Guinea Pigs; D008715:Methionine / Q000378:metabolism*; D010504:Periodic Acid / Q000494:pharmacology; D017433:Protein Structure, Secondary / Q000187:drug effects; D013388:Succinimides / Q000494:pharmacology
D003176:Complement C3; D003182:Complement C5; D004546:Elapid Venoms; D013388:Succinimides; C016310:cobra venom factor; C015752:N-chlorosuccinimide; D010504:Periodic Acid; D008715:Methionine; C009288:metaperiodate; D050577:Complement C3-C5 Convertases; D011415:Complement Factor B