Localization of the binding site for streptococcal protein G on human serum albumin. Identification of a 5.5-kilodalton protein G binding albumin fragment

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Protein G is a streptococcal cell wall protein with separate and repetitively arranged binding domains for immunoglobulin G (IgG) and human serum albumin (HSA). In this work, the binding of protein G to HSA was studied. The results suggest that a single binding site is present on HSA: the apparent size of the HSA-protein G complex (230 kDa) corresponded to two or three HSA molecules bound to one protein G molecule, and Ouchterlony immunodiffusion did not yield any precipitate between protein G and HSA. HSA was cleaved by pepsin and CNBr into several fragments which were identified by SDS-PAGE and N-terminal amino acid sequencing, and the binding of protein G to the fragments was studied in Western blot experiments. The results indicated that the binding area was located in disulfide loops 6-8, involving both the second (loop 6) and the third (loops 7 and 8) domain of HSA. One of the protein G binding pepsin fragments, with an apparent molecular mass of 5.5 kDa, located in loops 7 and 8, was isolated and found to completely inhibit the binding between protein G and the intact HSA, again suggesting a single protein G binding site on serum albumin. Reducing the disulfide bonds of HSA, and subsequent alkylation of the half-cystine residues, significantly decreased the affinity for protein G. Protein G bound to albumin from baboon, cat, guinea pig, hamster, hen, horse, man, mouse, and rat, but not to albumin from cow, dog, goat, pig, rabbit, sheep, snake, or turkey.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Medicinal Chemistry


  • Amino Acid Sequence, Animals, Binding Sites, Cats, Cattle, Cricetinae, Cyanogen Bromide, Dogs, Guinea Pigs, Horses, Humans, Male, Mice, Molecular Sequence Data, Molecular Weight, Nerve Tissue Proteins/chemistry, Papio, Pepsin A/metabolism, Peptide Fragments/chemistry, Peptide Mapping, Protein Binding, Protein Conformation, Rabbits, Rats, Serum Albumin/chemistry, Sheep, Species Specificity, Streptococcus/chemistry, Structure-Activity Relationship, Swine
Original languageEnglish
Pages (from-to)1451-7
Issue number5
Publication statusPublished - 1992 Feb 11
Publication categoryResearch