title: Analysis of recognition in the alternative pathway of complement. Effect of polysaccharide size.
abstract: Covalent attachment of the complement (C) protein C3b to polysaccharides on biologic particles which activate the alternative pathway leads to changes in the affinity of C3b for factor H, a regulatory protein of the C system. In this study the size of the site with which the polysaccharides interact and its special relationship to the thioester site were investigated using a fluorimetric assay and soluble C3b attached to low m.w. polysaccharides. Oligomers of alpha 1-6 and alpha 1-4 polyglucose and beta 1-2 polyfructose were prepared and attached to C3b at the thioester site. C3b bound to monomeric, dimeric, or trimeric sugars exhibited the same interaction with factor H as free C3b, i.e., there was no effect due to attachment alone. Beginning with tetrameric oligosaccharides a linear decrease in factor H binding was observed with increasing oligosaccharide size and the effect reached an apparent maximum with large polysaccharides. Maximum inhibition of factor H function was estimated to occur at a length of 16 saccharide units. The results suggest that this site, which regulates the inactivation rate of surface-bound C3b and thus the activation of the alternative pathway of C, spans a maximum of 13 sugar units (less than 65 A) starting four units (approximately 15 A) from the thioester site in C3b.
authors: Department of Biochemistry, University of Texas Health Center, Tyler 75710.
authors: M K
authors: MK
authors: Pangburn
mesh_terms: D001665:Binding Sites; D003167:Complement Activation; D003179:Complement C3b / Q000378:metabolism*; D003180:Complement C3b Inactivator Proteins / Q000378:metabolism; D017242:Complement Factor H; D003170:Complement Pathway, Alternative; D003911:Dextrans / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008070:Lipopolysaccharides / Q000494:pharmacology; D008970:Molecular Weight; D009844:Oligosaccharides / Q000032:analysis; D011134:Polysaccharides / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: C493495:CFH protein, human; D003180:Complement C3b Inactivator Proteins; D003911:Dextrans; D008070:Lipopolysaccharides; D009844:Oligosaccharides; D011134:Polysaccharides; D003179:Complement C3b; D017242:Complement Factor H