Crystal structure of human inosine triphosphatase: Substrate binding and implication of the itpa deficiency mutation p32T

Item Type:	Article
Title:	Crystal structure of human inosine triphosphatase: Substrate binding and implication of the itpa deficiency mutation p32T
Creators Name:	Stenmark, P. and Kursula, P. and Flodin, S. and Graeslund, S. and Landry, R. and Nordlund, P. and Schueler, H.
Abstract:	Inosine triphosphatase (ITPA) is a ubiquitous key regulator of cellular non-canonical nucleotide levels. It breaks down inosine and xanthine nucleotides generated by deamination of purine bases. Its enzymatic action prevents accumulation of ITP and reduces the risk of incorporation of potentially mutagenic inosine nucleotides into nucleic acids. Here we describe the crystal structure of human ITPA in complex with its prime substrate ITP, as well as the apo enzyme at 2.8 and 1.1 A, respectively. These structures show for the first time the site of substrate and Mg2+ coordination as well as the conformational changes accompanying substrate binding in this class of enzymes. Enzyme substrate interactions induce an extensive closure of the nucleotide binding grove, resulting in tight interactions with the base that explain the high substrate specificity of ITPA for inosine and xanthine over the canonical nucleotides. One of the dimer contact sites is made up by a loop that is involved in coordinating the metal ion in the active site. We predict that the ITPA deficiency mutation P32T leads to a shift of this loop that results in a disturbed affinity for nucleotides and/or a reduced catalytic activity in both monomers of the physiological dimer.
Keywords:	Amino Acid Substitution, Binding Sites, Complementary DNA, Crystallization, Molecular Cloning, Molecular Models, Mutation, Protein Conformation, Pyrophosphatases, Recombinant Proteins, Secondary Protein Structure, X-Ray Crystallography
Source:	Journal of Biological Chemistry
ISSN:	0021-9258
Publisher:	American Society for Biochemistry and Molecular Biology
Volume:	282
Number:	5
Page Range:	3182-3187
Date:	2 February 2007
Official Publication:	https://doi.org/10.1074/jbc.M609838200
PubMed:	View item in PubMed

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