title: Identification of peptidic inhibitors of the alternative complement pathway based on Staphylococcus aureus SCIN proteins.
abstract: The complement system plays a central role in a number of human inflammatory diseases, and there is a significant need for development of complement-directed therapies. The discovery of an arsenal of anti-complement proteins secreted by the pathogen Staphylococcus aureus brought with it the potential for harnessing the powerful inhibitory properties of these molecules. One such family of inhibitors, the SCINs, interact with a functional "hot-spot" on the surface of C3b. SCINs not only stabilize an inactive form of the alternative pathway (AP) C3 convertase (C3bBb), but also overlap the C3b binding site of complement factors B and H. Here we determined that a conserved Arg residue in SCINs is critical for function of full-length SCIN proteins. Despite this, we also found SCIN-specific differences in the contributions of other residues found at the C3b contact site, which suggested that a more diverse repertoire of residues might be able to recognize this region of C3b. To investigate this possibility, we conducted a phage display screen aimed at identifying SCIN-competitive 12-mer peptides. In total, seven unique sequences were identified and all exhibited direct C3b binding. A subset of these specifically inhibited the AP in assays of complement function. The mechanism of AP inhibition by these peptides was probed through surface plasmon resonance approaches, which revealed that six of the seven peptides disrupted C3bBb formation by interfering with factor B/C3b binding. To our knowledge this study has identified the first small molecules that retain inhibitory properties of larger staphylococcal immune evasion proteins.
authors.affiliation: School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, United States.
authors.forename: Brady J
authors.initials: BJ
authors.lastname: Summers
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, KS 66506, United States.
authors.forename: Brandon L
authors.initials: BL
authors.lastname: Garcia
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, KS 66506, United States.
authors.forename: Jordan L
authors.initials: JL
authors.lastname: Woehl
authors.affiliation: Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, KS 66506, United States.
authors.forename: Kasra X
authors.initials: KX
authors.lastname: Ramyar
authors.affiliation: School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, United States.
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Yao
authors.affiliation: School of Biological Sciences, University of Missouri-Kansas City, Kansas City, MO 64110, United States; Department of Biochemistry & Molecular Biophysics, Kansas State University, Manhattan, KS 66506, United States. Electronic address: geisbrechtb@k-state.edu.
authors.forename: Brian V
authors.initials: BV
authors.lastname: Geisbrecht
mesh_terms: D000818:Animals; D001120:Arginine / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D051561:Complement C3 Convertase, Alternative Pathway; D003179:Complement C3b / Q000378:metabolism; D011415:Complement Factor B / Q000378:metabolism; D003170:Complement Pathway, Alternative / Q000187:drug effects*; D017124:Conserved Sequence; D006801:Humans; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D019151:Peptide Library; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D017433:Protein Structure, Secondary; D011817:Rabbits; D012996:Solutions; D013211:Staphylococcus aureus / Q000378:metabolism*; D020349:Surface Plasmon Resonance
chemical_list: D001426:Bacterial Proteins; D050505:Mutant Proteins; D019151:Peptide Library; D010455:Peptides; D012996:Solutions; D003179:Complement C3b; D001120:Arginine; D051561:Complement C3 Convertase, Alternative Pathway; D011415:Complement Factor B
keywords: Alternative pathway C3 convertase; Complement; Inhibitors; Peptides; Surface plasmon resonance