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The effect of residue 1106 on the thioester‐mediated covalent binding reaction of human complement protein C4 and the monomeric rat α‐macroglobulin α 1 I3
Author(s) -
Ren Xiang-Dong,
Dodds Alister W.,
Enghild Jan J.,
Chu Charleen T.,
Alex Law S.K.
Publication year - 1995
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(95)00606-a
Subject(s) - thioester , monomer , residue (chemistry) , chemistry , covalent bond , covalent binding , macroglobulin , complement system , biochemistry , stereochemistry , organic chemistry , biology , antibody , enzyme , polymer , immunology
The histidine at position 1106 of the C4B isotype of human complement is involved in catalyzing the covalent binding of the thioester to glycerol and water. By replacing the histidine with other residues, it was found that tyrosine is also capable of mediating the reaction. We propose that they act as nucleophiles by first attacking the thioester, upon activation, to form acyl intermediates, which subsequently react with the hydroxyl groups of glycerol or water. The monomeric α‐macroglobulin, α 1 I3 of the rat, was also studied. Unlike α 2 ‐macroglobulin, which is a tetramer, α 1 I3 has binding properties similar to those of C4A.