Browsing by Author "Acharya, K Ravi"

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    Crystal structure of protoporphyrinogen oxidase from Myxococcus xanthus and its complex with the inhibitor acifluorfen
    (American Society for Biochemistry and Molecular Biology, 2006) Corradi, Hazel R; Corrigall, Anne V; Boix, Ester; Mohan, C Gopi; Sturrock, Edward D; Meissner, Peter N; Acharya, K Ravi
    Protoporphyrinogen IX oxidase, a monotopic membrane protein, which catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX in the heme/chlorophyll biosynthetic pathway, is distributed widely throughout nature. Here we present the structure of protoporphyrinogen IX oxidase from Myxococcus xanthus, an enzyme with similar catalytic properties to human protoporphyrinogen IX oxidase that also binds the common plant herbicide, acifluorfen. In the native structure, the planar porphyrinogen substrate is mimicked by a Tween 20 molecule, tracing three sides of the macrocycle. In contrast, acifluorfen does not mimic the planarity of the substrate but is accommodated by the shape of the binding pocket and held in place by electrostatic and aromatic interactions. A hydrophobic patch surrounded by positively charged residues suggests the position of the membrane anchor, differing from the one proposed for the tobacco mitochondrial protoporphyrinogen oxidase. Interestingly, there is a discrepancy between the dimerization state of the protein in solution and in the crystal. Conserved structural features are discussed in relation to a number of South African variegate porphyria-causing mutations in the human enzyme.
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    Crystal structure of the N domain of human somatic angiotensin I-converting enzyme provides a structural basis for domain-specific inhibitor design
    (Elsevier, 2006) Corradi, Hazel R; Schwager, Sylva L U; Nchinda, Aloysius T; Sturrock, Edward D; Acharya, K Ravi
    Human somatic angiotensin I-converting enzyme (sACE) is a key regulator of blood pressure and an important drug target for combating cardiovascular and renal disease. sACE comprises two homologous metallopeptidase domains, N and C, joined by an inter-domain linker. Both domains are capable of cleaving the two hemoregulatory peptides angiotensin I and bradykinin, but differ in their affinities for a range of other substrates and inhibitors. Previously we determined the structure of testis ACE (C domain); here we present the crystal structure of the N domain of sACE (both in the presence and absence of the antihypertensive drug lisinopril) in order to aid the understanding of how these two domains differ in specificity and function. In addition, the structure of most of the inter-domain linker allows us to propose relative domain positions for sACE that may contribute to the domain cooperativity. The structure now provides a platform for the design of “domain-specific” second-generation ACE inhibitors.
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    Structural details on the binding of antihypertensive drugs captopril and enalaprilat to human testicular angiotensin I-converting enzyme
    (American Chemical Society, 2004) Natesh, Ramanathan; Schwager, Sylva L U; Evans, Hazel R; Sturrock, Edward D; Acharya, K Ravi
    Angiotensin converting enzyme (ACE) plays a critical role in the circulating or endocrine renin−angiotensin system (RAS) as well as the local regulation that exists in tissues such as the myocardium and skeletal muscle. Here we report the high-resolution crystal structures of testis ACE (tACE) in complex with the first successfully designed ACE inhibitor captopril and enalaprilat, the Phe-Ala-Pro analogue. We have compared these structures with the recently reported structure of a tACE−lisinopril complex [Natesh et al. (2003) Nature 421, 551−554]. The analyses reveal that all three inhibitors make direct interactions with the catalytic Zn2+ ion at the active site of the enzyme:  the thiol group of captopril and the carboxylate group of enalaprilat and lisinopril. Subtle differences are also observed at other regions of the binding pocket. These are compared with N-domain models and discussed with reference to published biochemical data. The chloride coordination geometries of the three structures are discussed and compared with other ACE analogues. It is anticipated that the molecular details provided by these structures will be used to improve the binding and/or the design of new, more potent domain-specific inhibitors of ACE that could serve as new generation antihypertensive drugs.
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    The structure of testis angiotensin-converting enzyme in complex with the C domain-specific inhibitor RXPA380
    (American Chemical Society, 2007) Corradi, Hazel R; Chitapi, Itai; Sewell, B Trevor; Georgiadis, Dimitris; Dive, Vincent; Sturrock, Edward D; Acharya, K Ravi
    Angiotensin I-converting enzyme (ACE) is central to the regulation of the renin−angiotensin system and is a key therapeutic target for combating hypertension and related cardiovascular diseases. Currently available drugs bind both active sites of its two homologous domains, although it is now understood that these domains function differently in vivo. The recently solved crystal structures of both domains (N and C) open the door to new domain-specific inhibitor design, taking advantage of the differences between these two large active sites. Here we present the first crystal structure at a resolution of 2.25 Å of testis ACE (identical to the C domain of somatic ACE) with the highly C-domain-specific phosphinic inhibitor, RXPA380. Testis ACE retains the same conformation as seen in previously determined inhibitor complexes, but the RXPA380 central backbone conformation is more similar to that seen for the inhibitor captopril than enalaprilat. The RXPA380 molecule occupies more subsites of the testis ACE active site than the previously determined inhibitors and possesses bulky moieties that extend into the S2‘ and S2 subsites. Thus the high affinity of RXPA380 for the testis ACE/somatic ACE C domain is explained by the interaction of these bulky moieties with residues unique to these domains, specifically Phe 391, Val 379, and Val 380, that are not found in the N domain. The characterization of the extended active site and the binding of a potent C-domain-selective inhibitor provide the first structural data for the design of truly domain-specific pharmacophores.