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Human guanine monophosphate synthetase

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PDB Code 2VXO Target Class Nucleotide metabolism Target GMPS Alias GMPS Disease Area/Function cancer Date Deposited Jul 08 2008 Authors M.WELIN, L.LEHTIO, J.ANDERSSON, C.H.ARROWSMITH, H.BERGLUND, R.COLLINS, L.G.DAHLGREN, A.M.EDWARDS, S.FLODIN, A.FLORES, S.GRASLUND, M.HAMMARSTROM, A.JOHANSSON, I.JOHANSSON, T.KARLBERG, T.KOTENYOVA, M.MOCHE, M.E.NILSSON, T.NYMAN, K.OLESEN, C.PERSSON, J.SAGEMARK, H.SCHUELER, A.G.THORSELL, L.TRESAUGUES, S.VAN DEN BERG, M.WISNIEWSKA, M.WIKSTROM, P.NORDLUND Related Structure 2VPI

About this structure

GMP synthetase (GMPS, E.C. 6.3.5.2) is a glutamine amidotransferase involved in the de novo synthesis of purines. It catalyzes the conversion xanthosine 5'-monophosphate to guanosine 5'-monophosphate in the presence of glutamine and ATP. GMPS is a bifunctional enzyme with two domains, an N-terminal glutaminase domain that generates ammonia from glutamine, and a C-terminal synthetase domain that in turn aminates XMP to form GMP [1].

XMP + ATP + GLN + H2O -> GMP + AMP + GLU + PPi

GMPS has been observed to have increased activity in rapidly proliferating cells and is thus a potential target for anticancer therapies using for example glutamine analogs, like acivicin has been shown to inhibit GMPS [2,3,4]. The structure of the E. coli GMPS revealed that the active sites of the two domains are separated by 30 Å, but no obvious route for the ammonia transfer could be obtained. Instead large movements between the domains during reaction have been suggested [1,5].

Here we have solved the structure of the human GMP synthetase to a resolution of 2.5 Å. The structure was solved with molecular replacement using the two domains separately, the glutaminase domain of human GMP synthetase (pdb-code: 2VPI) and the synthetase domain of Thermus thermophilus (pdb-code: 2YWC) were used as search models. GMPS belongs to the class 1 glutamine dependent amidotranferases which has a conserved catalytic triad consisting of a Cys-His-Glu [5]. The asymmetric unit contains a homodimer with an XMP molecule bound to each active site. The human GMPS is slightly larger than the T. thermophilus GMPS and E.coli GMPS structures, having an additional domain stretching from residue 449 to residue 579. This domain is built up by a three stranded -sheet flanked by five -helices. A -hairpin in this domain is also interacting with the same -hairpin in the other subunit and involved in binding of the phosphate moiety of XMP. Parts of this domain are also in the dimer interface. While the dimers of the bacterial structures are more open the human GMPS dimer is more tightly packed. This is the first GMPS structure of eukaryotic origin and the information regarding substrate binding will aid potential drug design.

References

  1. Huang X, Holden HM, Raushel FM. Channeling of substrates and intermediates in enzyme-catalyzed reactions. Annu Rev Biochem. 2001;70:149-80.
  2. Hirst M, Haliday E, Nakamura J, Lou L. Human GMP synthetase. Protein purification, cloning, and functional expression of cDNA.. J Biol Chem. 1994 Sep 23;269(38):23830-7.
  3. Nakamura J, Straub K, Wu J, Lou L. The glutamine hydrolysis function of human GMP synthetase. Identification of an essential active site cysteine. J Biol Chem. 1995 Oct 6;270(40):23450-5.
  4. Chittur SV, Klem TJ, Shafer CM, Davisson VJ. Mechanism for acivicin inactivation of triad glutamine amidotransferases. Biochemistry. 2001 Jan 30;40(4):876-87.
  5. Tesmer JJ, Klem TJ, Deras ML, Davisson VJ, Smith JL. The crystal structure of GMP synthetase reveals a novel catalytic triad and is a structural paradigm for two enzyme families. Nat Struct Biol. 1996 Jan;3(1):74-86.