Fu Q, McPhie P, Gowda D C
Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, Washington, DC 20007, USA.
Biochem Mol Biol Int. 1998 Jun;45(1):133-44. doi: 10.1080/15216549800202502.
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.
在0℃下用5 mM高碘酸钠处理2分钟内，眼镜蛇毒因子（CVF）介导的豚鼠红细胞补体介导裂解减少了50 - 60%。这种活性丧失与3 - 4个甲硫氨酸的修饰平行；寡糖链的其他氨基酸和糖残基未受影响。在特异性修饰3 - 4个易氧化甲硫氨酸的条件下，用N - 氯代琥珀酰亚胺或氯胺 - T处理也导致CVF活性丧失50 - 60%。这些修饰未改变CVF的二级结构。甲硫氨酸修饰的CVF（MetCVF）支持因子D裂解因子B，其效率与未处理的CVF相同，以形成替代途径的C3/C5转化酶（MetCVF，Bb）。MetCVF，Bb和CVF，Bb在C3裂解方面没有区别。然而，MetCVF，Bb的C5裂解能力明显低于CVF，Bb。这些结果表明甲硫氨酸参与了CVF与C5的结合。
