title: Critical roles of Asp40 at the haem proximal side of haem-regulated phosphodiesterase from Escherichia coli in redox potential, auto-oxidation and catalytic control.
abstract: In haem-regulated phosphodiesterase (PDE) from Escherichia coli (Ec DOS), haem is bound to the PAS domain, and the redox state of the haem iron regulates catalysis by the PDE domain. We generated mutants of Asp40, which forms a hydrogen bond with His77 (a proximal haem axial ligand) via two water molecules, and a salt bridge with Arg85 at the protein surface. The redox potential of haem was markedly increased from 67 mV vs. the standard hydrogen electrode in the wild-type enzyme to 95 mV and 114 mV in the Ala and Asn mutants, respectively. Additionally, the auto-oxidation rate of Ec DOS PAS was significantly increased from 0.0053 to 0.051 and 0.033 min(-1), respectively. Interestingly, the catalytic activities of the Asp40 mutants were abolished completely. Thus, Asp40 appears to play a critical role in the electronic structure of the haem iron and redox-dependent catalytic control of the PDE domain. In this report, we discuss the mechanism of catalytic control of Ec DOS, based on the physico-chemical characteristics of the Asp40 mutants.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Watanabe
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Kurokawa
authors.forename: Tokiko
authors.initials: T
authors.lastname: Yoshimura-Suzuki
authors.forename: Ikuko
authors.initials: I
authors.lastname: Sagami
authors.forename: Toru
authors.initials: T
authors.lastname: Shimizu
mesh_terms: D001224:Aspartic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002384:Catalysis; D020134:Catalytic Domain; D004926:Escherichia coli / Q000201:enzymology*; D006418:Heme / Q000737:chemistry*; D006860:Hydrogen Bonding; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics*; D010084:Oxidation-Reduction; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D001224:Aspartic Acid; D006418:Heme; D010727:Phosphoric Diester Hydrolases