The complement system proteins C3 and C4 and the plasma protease inhibitor α2-macroglobulin~ when activated by limited proteolysis, can bind covalently to other macromolecules. The three proteins also exhibit an unusual internal peptide-bond cleavage reaction when denatured. The covalent binding reaction is likely to occur by a transacylation mechanism involving an internal thioiester in the three proteins. However, the activated species of these proteins are much more reactive than simple thiolesters. Studies of molecular models of the thiolester region in C3 show that an intramolecular acid catalysis mechanism can both account for the exceptional reactivity of the activated form of these proteins and provide an explanation for the denaturation-induced peptide bond cleavage.
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June 01 1981
Intramolecular general acid catalysis in the binding reactions of α2 and complement components C3 and C4
Stephen G. Davies;
Stephen G. Davies
*The Dyson Perrins Laboratory, South Parks Road, Oxford OX1 3QY, U.K.
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Robert B. Sim
Robert B. Sim
†MRC Immunochemistry Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.
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Publisher: Portland Press Ltd
Received:
May 20 1981
Online ISSN: 1573-4935
Print ISSN: 0144-8463
© 1981 The Biochemical Society
1981
Biosci Rep (1981) 1 (6): 461–468.
Article history
Received:
May 20 1981
Citation
Stephen G. Davies, Robert B. Sim; Intramolecular general acid catalysis in the binding reactions of α2 and complement components C3 and C4. Biosci Rep 1 June 1981; 1 (6): 461–468. doi: https://doi.org/10.1007/BF01121579
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