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标题：Complement C3 convertase: Cell surface restriction of β1H control and generation of restriction on neuraminidase-treated cells
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作者：Michael K. Pangburn ; Hans J. Müller-Eberhard
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：5
页码：2416-2420
DOI：10.1073/pnas.75.5.2416
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The alternative or properdin pathway of complement is primarily controlled by the endopeptidase C3b inactivator (C3bINA) and the nonproteolytic glycoprotein {beta}1H. The molecular mechanisms of control were investigated by performing binding studies of radiolabeled complement proteins to C3b bearing sheep erythrocytes (ESC3b). C3b was found to have distinct binding sites for {beta}1H, C3bINA, Factor B, and properdin. {beta}1H binding increased C3bINA binding 30-fold, while Factor B binding prevented C3bINA action on C3b and was competitive with {beta}1H binding. Properdin binding, which facilitates Factor B interaction with C3b, had no effect on the {beta}1H and C3bINA sites. Activators such as rabbit erythrocytes (ER) have previously been shown to interfere with the effectiveness of the control by C3bINA and {beta}1H, thereby allowing unrestricted formation of C3 convertase. Such restriction of control does not occur on the surface of ES, a nonactivator of the alternative pathway. On the basis of comparative binding studies, restriction of control is explained entirely by reduced binding of {beta}1H to ERC3b relative to ESC3b. Access of properdin, Factor B, C3bINA, and the Fab fragment of anti-C3 to the two cell types was unrestricted. Restriction of {beta}1H control could be generated on the surface of ES by removal of cell-surface sialic acid with neuraminidase (acylneuraminyl hydrolase; EC 3.2.1.18 ). This enzymatic treatment converted ES from a nonactivator to an activator of the alternative pathway.
关键词：alternative pathway ; properdin ; cell membranes ; protein-protein interactions ; C3b inactivator