title: Structural Basis for Simvastatin Competitive Antagonism of Complement Receptor 3.
abstract: The complement system is an important part of the innate immune response to infection but may also cause severe complications during inflammation. Small molecule antagonists to complement receptor 3 (CR3) have been widely sought, but a structural basis for their mode of action is not available. We report here on the structure of the human CR3 ligand-binding I domain in complex with simvastatin. Simvastatin targets the metal ion-dependent adhesion site of the open, ligand-binding conformation of the CR3 I domain by direct contact with the chelated Mg(2+) ion. Simvastatin antagonizes I domain binding to the complement fragments iC3b and C3d but not to intercellular adhesion molecule-1. By virtue of the I domain's wide distribution in binding kinetics to ligands, it was possible to identify ligand binding kinetics as discriminator for simvastatin antagonism. In static cellular experiments, 15-25 μm simvastatin reduced adhesion by K562 cells expressing recombinant CR3 and by primary human monocytes, with an endogenous expression of this receptor. Application of force to adhering monocytes potentiated the effects of simvastatin where only a 50-100 nm concentration of the drug reduced the adhesion by 20-40% compared with untreated cells. The ability of simvastatin to target CR3 in its ligand binding-activated conformation is a novel mechanism to explain the known anti-inflammatory effects of this compound, in particular because this CR3 conformation is found in pro-inflammatory environments. Our report points to new designs of CR3 antagonists and opens new perspectives and identifies druggable receptors from characterization of the ligand binding kinetics in the presence of antagonists.
authors.affiliation: From the Departments of Biomedicine.
authors.forename: Maria Risager
authors.initials: MR
authors.lastname: Jensen
authors.affiliation: Molecular Biology and Genetics, and the Lundbeck Foundation Nanomedicine Center for Individualized Management of Tissue Damage and Regeneration (LUNA), and.
authors.forename: Goran
authors.identifier: 0000-0003-0480-4324
authors.initials: G
authors.lastname: Bajic
authors.affiliation: From the Departments of Biomedicine.
authors.forename: Xianwei
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Chemistry, the Interdisciplinary Nanoscience Center (iNANO).
authors.forename: Anne Kjær
authors.initials: AK
authors.lastname: Laustsen
authors.affiliation: Chemistry, the Interdisciplinary Nanoscience Center (iNANO), the Center for Insoluble Protein Structures (inSPIN).
authors.forename: Heidi
authors.initials: H
authors.lastname: Koldsø
authors.affiliation: Chemistry, the Interdisciplinary Nanoscience Center (iNANO), the Center for Insoluble Protein Structures (inSPIN).
authors.forename: Katrine Kirkeby
authors.identifier: 0000-0003-4893-6003
authors.initials: KK
authors.lastname: Skeby
authors.affiliation: Chemistry, the Interdisciplinary Nanoscience Center (iNANO), the Center for Insoluble Protein Structures (inSPIN).
authors.forename: Birgit
authors.identifier: 0000-0001-9937-1562
authors.initials: B
authors.lastname: Schiøtt
authors.affiliation: Molecular Biology and Genetics, and the Lundbeck Foundation Nanomedicine Center for Individualized Management of Tissue Damage and Regeneration (LUNA), and.
authors.forename: Gregers R
authors.identifier: 0000-0001-6292-3319
authors.initials: GR
authors.lastname: Andersen
authors.affiliation: From the Departments of Biomedicine, the Lundbeck Foundation Nanomedicine Center for Individualized Management of Tissue Damage and Regeneration (LUNA), and the Interdisciplinary Nanoscience Center (iNANO), the MEMBRANES Research Center, Aarhus University, DK-8000 Aarhus C, Denmark vorup-jensen@biomed.au.dk.
authors.forename: Thomas
authors.initials: T
authors.lastname: Vorup-Jensen
mesh_terms: D003179:Complement C3b / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D016177:Macrophage-1 Antigen / Q000737:chemistry / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism; D009000:Monocytes / Q000378:metabolism*; D000072417:Protein Domains; D019821:Simvastatin / Q000737:chemistry / Q000494:pharmacology
chemical_list: D016177:Macrophage-1 Antigen; D003179:Complement C3b; D019821:Simvastatin; D008274:Magnesium
keywords: anti-inflammatory therapy; cell adhesion; complement; inflammation; integrin; molecular dynamics; protein drug interaction; receptor structure-function; statin; surface plasmon resonance (SPR)