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      Structure and Mechanism of the Bifunctional CinA Enzyme from Thermus thermophilus *

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          Abstract

          Background: CinA is a bifunctional enzyme that catalyzes reactions associated with pyridine nucleotide recycling in bacteria.

          Results: the structure of the enzyme shows an unusual asymmetric dimer with one of the catalytic sites in two different conformational states.

          Conclusion: Mechanisms for both reactions are proposed, based on structures of ligand complexes.

          Significance: Asymmetric enzyme dimers are rare; in this case, domain movement is necessary to promote catalysis.

          Abstract

          CinA is a widely distributed protein in Gram-positive and Gram-negative bacteria. It is associated with natural competence and is proposed to have a function as an enzyme participating in the pyridine nucleotide cycle, which recycles products formed by non-redox uses of NAD. Here we report the determination of the crystal structure of CinA from Thermus thermophilus, in complex with several ligands. CinA was shown to have both nicotinamide mononucleotide deamidase and ADP-ribose pyrophosphatase activities. The crystal structure shows an unusual asymmetric dimer, with three domains for each chain; the C-terminal domain harbors the nicotinamide mononucleotide deamidase activity, and the structure of a complex with the product nicotinate mononucleotide suggests a mechanism for deamidation. The N-terminal domain belongs to the COG1058 family and is associated with the ADP-ribose pyrophosphatase activity. The asymmetry in the CinA dimer arises from two alternative orientations of the COG1058 domains, only one of which forms a contact with the KH-type domain from the other chain, effectively closing the active site into, we propose, a catalytically competent state. Structures of complexes with Mg 2+/ADP-ribose, Mg 2+/ATP, and Mg 2+/AMP suggest a mechanism for the ADP-ribose pyrophosphatase reaction that involves a rotation of the COG1058 domain dimer as part of the reaction cycle, so that each active site oscillates between open and closed forms, thus promoting catalysis.

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          Most cited references23

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          Structural symmetry and protein function.

          The majority of soluble and membrane-bound proteins in modern cells are symmetrical oligomeric complexes with two or more subunits. The evolutionary selection of symmetrical oligomeric complexes is driven by functional, genetic, and physicochemical needs. Large proteins are selected for specific morphological functions, such as formation of rings, containers, and filaments, and for cooperative functions, such as allosteric regulation and multivalent binding. Large proteins are also more stable against denaturation and have a reduced surface area exposed to solvent when compared with many individual, smaller proteins. Large proteins are constructed as oligomers for reasons of error control in synthesis, coding efficiency, and regulation of assembly. Symmetrical oligomers are favored because of stability and finite control of assembly. Several functions limit symmetry, such as interaction with DNA or membranes, and directional motion. Symmetry is broken or modified in many forms: quasisymmetry, in which identical subunits adopt similar but different conformations; pleomorphism, in which identical subunits form different complexes; pseudosymmetry, in which different molecules form approximately symmetrical complexes; and symmetry mismatch, in which oligomers of different symmetries interact along their respective symmetry axes. Asymmetry is also observed at several levels. Nearly all complexes show local asymmetry at the level of side chain conformation. Several complexes have reciprocating mechanisms in which the complex is asymmetric, but, over time, all subunits cycle through the same set of conformations. Global asymmetry is only rarely observed. Evolution of oligomeric complexes may favor the formation of dimers over complexes with higher cyclic symmetry, through a mechanism of prepositioned pairs of interacting residues. However, examples have been found for all of the crystallographic point groups, demonstrating that functional need can drive the evolution of any symmetry.
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            The Nudix hydrolase superfamily.

            Nudix hydrolases are found in all classes of organism and hydrolyse a wide range of organic pyrophosphates, including nucleoside di- and triphosphates, dinucleoside and diphosphoinositol polyphosphates, nucleotide sugars and RNA caps, with varying degrees of substrate specificity. Some superfamily members, such as Escherichia coli MicrotT, have the ability to degrade potentially mutagenic, oxidised nucleotides while others control the levels of metabolic intermediates and signalling compounds. In prokaryotes and simple eukaryo tes, the number of Nudix genes varies from 0 to over 30, reflecting the metabolic complexity and adaptability of the organism. Mammals have around 24 Nudix genes, several of which encode more than one variant. This review integrates the sizeable recent literature on these proteins with information from global functional genomic studies to provide some insights into the possible roles of different superfamily members in cellular metabolism and homeostasis and to stimulate discussion and further research into this ubiquitous protein family.
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              Developments in the CCP4 molecular-graphics project.

              Progress towards structure determination that is both high-throughput and high-value is dependent on the development of integrated and automatic tools for electron-density map interpretation and for the analysis of the resulting atomic models. Advances in map-interpretation algorithms are extending the resolution regime in which fully automatic tools can work reliably, but at present human intervention is required to interpret poor regions of macromolecular electron density, particularly where crystallographic data is only available to modest resolution [for example, I/sigma(I) < 2.0 for minimum resolution 2.5 A]. In such cases, a set of manual and semi-manual model-building molecular-graphics tools is needed. At the same time, converting the knowledge encapsulated in a molecular structure into understanding is dependent upon visualization tools, which must be able to communicate that understanding to others by means of both static and dynamic representations. CCP4 mg is a program designed to meet these needs in a way that is closely integrated with the ongoing development of CCP4 as a program suite suitable for both low- and high-intervention computational structural biology. As well as providing a carefully designed user interface to advanced algorithms of model building and analysis, CCP4 mg is intended to present a graphical toolkit to developers of novel algorithms in these fields.
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                Author and article information

                Journal
                J Biol Chem
                J. Biol. Chem
                jbc
                jbc
                JBC
                The Journal of Biological Chemistry
                American Society for Biochemistry and Molecular Biology (9650 Rockville Pike, Bethesda, MD 20814, U.S.A. )
                0021-9258
                1083-351X
                28 November 2014
                13 October 2014
                13 October 2014
                : 289
                : 48
                : 33187-33197
                Affiliations
                [1]From the Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, United Kingdom
                Author notes
                [1 ] To whom correspondence should be addressed. Tel.: 44-161-306-4207; E-mail: Jeremy.Derrick@ 123456manchester.ac.uk .
                Article
                M114.608448
                10.1074/jbc.M114.608448
                4246079
                25313401
                67dc6c3c-8b6e-47dc-8a4c-60b66f402630
                © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

                Author's Choice—Final version full access.

                Creative Commons Attribution Unported License applies to Author Choice Articles

                History
                : 2 September 2014
                : 8 October 2014
                Categories
                Enzymology

                Biochemistry
                dna transformation,enzyme catalysis,hydrolase,nicotinamide adenine dinucleotide (nad),x-ray crystallography,adp-ribose pyrophosphatase,cog1058 domain,nicotinamide mononucleotide deamidase

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