title: Crystal structure of human arginase I at 1.29-A resolution and exploration of inhibition in the immune response.
abstract: Human arginase I is a potential target for therapeutic intervention in diseases linked to compromised l-arginine homeostasis. Here, we report high-affinity binding of the reaction coordinate analogue inhibitors 2(S)-amino-6-boronohexanoic acid (ABH, Kd = 5 nM) and S-(2-boronoethyl)-l-cysteine (BEC, Kd = 270 nM) to human arginase I, and we report x-ray crystal structures of the respective enzyme-inhibitor complexes at 1.29- and 1.94-A resolution determined from crystals twinned by hemihedry. The ultrahigh-resolution structure of the human arginase I-ABH complex yields an unprecedented view of the binuclear manganese cluster and illuminates the structural basis for nanomolar affinity: bidentate inner-sphere boronate-manganese coordination interactions and fully saturated hydrogen bond networks with inhibitor alpha-amino and alpha-carboxylate groups. These interactions are therefore implicated in the stabilization of the transition state for l-arginine hydrolysis. Electron density maps also reveal that active-site residue H141 is protonated as the imidazolium cation. The location of H141 is such that it could function as a general acid to protonate the leaving amino group of l-ornithine during catalysis, and this is a revised mechanistic proposal for arginase. This work serves as a foundation for studying the structural and chemical biology of arginase I in the immune response, and we demonstrate the inhibition of arginase activity by ABH in human and murine myeloid cells.
authors.affiliation: Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: Di Costanzo
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Sabio
authors.forename: Alfonso
authors.initials: A
authors.lastname: Mora
authors.forename: Paulo C
authors.initials: PC
authors.lastname: Rodriguez
authors.forename: Augusto C
authors.initials: AC
authors.lastname: Ochoa
authors.forename: Francisco
authors.initials: F
authors.lastname: Centeno
authors.forename: David W
authors.initials: DW
authors.lastname: Christianson
mesh_terms: D000614:Aminocaproates / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D001119:Arginase / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D001665:Binding Sites; D001896:Boron Compounds / Q000737:chemistry / Q000494:pharmacology; D002384:Catalysis; D002478:Cells, Cultured; D018360:Crystallography, X-Ray; D006801:Humans; D007109:Immunity / Q000187:drug effects*; D017737:Macrophages, Peritoneal / Q000276:immunology; D008345:Manganese / Q000737:chemistry; D051379:Mice; D015394:Molecular Structure; D022423:Myeloid Cells / Q000276:immunology
chemical_list: C121228:2-amino-6-boronohexanoic acid; D000614:Aminocaproates; D001896:Boron Compounds; D008345:Manganese; D001119:Arginase