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Structural studies of tri-functional human GART
Authors:Martin Welin  J?rg Günter Grossmann  Susanne Flodin  Tomas Nyman  P?l Stenmark  Lionel Trésaugues  Tetyana Kotenyova  Ida Johansson  P?r Nordlund  Lari Lehti?
Institution:1Structural Genomics Consortium, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden, 2Molecular Biophysics Group, School of Biological Sciences, The University of Liverpool, Liverpool L69 7ZB, UK and 3Pharmaceutical Sciences, Department of Biosciences, Åbo Akademi University, 20520 Turku, Finland
Abstract:Human purine de novo synthesis pathway contains several multi-functional enzymes, one of which, tri-functional GART, contains three enzymatic activities in a single polypeptide chain. We have solved structures of two domains bearing separate catalytic functions: glycinamide ribonucleotide synthetase and aminoimidazole ribonucleotide synthetase. Structures are compared with those of homologous enzymes from prokaryotes and analyzed in terms of the catalytic mechanism. We also report small angle X-ray scattering models for the full-length protein. These models are consistent with the enzyme forming a dimer through the middle domain. The protein has an approximate seesaw geometry where terminal enzyme units display high mobility owing to flexible linker segments. This resilient seesaw shape may facilitate internal substrate/product transfer or forwarding to other enzymes in the pathway.
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