title: Molecular basis of C-reactive protein binding and modulation of complement activation by factor H-related protein 4.
abstract: C-reactive protein (CRP) is a pattern recognition molecule that binds several microbial and host ligands. Ligand-bound CRP activates the complement system via the classical pathway. Previously, we identified human complement factor H-related protein 4 (CFHR4), a member of the factor H protein family, as a CRP binding protein. Here, we investigated the molecular basis and the functional relevance of the interaction of CFHR4 with native CRP. Using recombinantly expressed CFHR4 fragments, the CRP binding site was localized to the first short consensus repeat (SCR) domain of CFHR4. Peptide arrays identified residues 35-41 of CFHR4 to be involved in CRP binding. Substitutions of the positively charged amino acids of this motif resulted in strongly reduced CRP binding. Sequence comparisons revealed that such a motif is not present in the related SCR6 domain of factor H, or in the homologous domains of the four other CFHR proteins. Homology modelling based on SCR6 of factor H showed that the CRP binding site is surface exposed on SCR1 of CFHR4. CFHR4-bound CRP was able to activate complement, determined by C3 fragment deposition. Recombinant CFHR4 proteins with mutations in the identified binding site showed reduced CRP binding, which in turn resulted in reduced complement activation. In summary, these data reveal the molecular basis of the specific interaction of CFHR4 with native CRP and suggest a role for CFHR4 in enhancing opsonization via CRP binding.
authors.affiliation: Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute, Jena, Germany.
authors.forename: Mario
authors.initials: M
authors.lastname: Hebecker
authors.forename: Azubuike I
authors.initials: AI
authors.lastname: Okemefuna
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Perkins
authors.forename: Michael
authors.initials: M
authors.lastname: Mihlan
authors.forename: Markus
authors.initials: M
authors.lastname: Huber-Lang
authors.forename: Mihály
authors.initials: M
authors.lastname: Józsi
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000494:pharmacology; D001053:Apolipoproteins / Q000737:chemistry* / Q000276:immunology*; D001665:Binding Sites; D002097:C-Reactive Protein / Q000378:metabolism*; D003167:Complement Activation / Q000187:drug effects / Q000276:immunology*; D003176:Complement C3 / Q000276:immunology; D016384:Consensus Sequence; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D040081:Protein Array Analysis; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid
chemical_list: D000596:Amino Acids; D001053:Apolipoproteins; C105092:CFHR4 protein, human; D003176:Complement C3; D050505:Mutant Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D002097:C-Reactive Protein