A novel context for the 'MutT' module, a guardian of cell integrity, in a diphosphoinositol polyphosphate phosphohydrolase.
Diphosphoinositol pentakisphosphate (PP-InsP5 or 'InsP7') and bisdiphosphoinositol tetrakisphosphate ([PP]2-InsP4 or 'InsP8') are the most highly phosphorylated members of the inositol-based cell signaling family. We have purified a rat hepatic diphosphoinositol polyphosphate phosphohydrolase (DIPP) that cleaves a beta-phosphate from the diphosphate groups in PP-InsP5 (Km = 340 nM) and [PP]2-InsP4 (Km = 34 nM). Inositol hexakisphophate (InsP6) was not a substrate, but it inhibited metabolism of both [PP]2-InsP4 and PP-InsP5 (IC50 = 0.2 and 3 microM, respectively). Microsequencing of DIPP revealed a 'MutT' domain, which in other contexts guards cellular integrity by dephosphorylating 8-oxo-dGTP, which causes AT to CG transversion mutations. The MutT domain also metabolizes some nucleoside phosphates that may play roles in signal transduction. The rat DIPP MutT domain is conserved in a novel recombinant human uterine DIPP. The nucleotide sequence of the human DIPP cDNA was aligned to chromosome 6; the candidate gene contains at least four exons. The dependence of DIPP's catalytic activity upon its MutT domain was confirmed by mutagenesis of a conserved glutamate residue. DIPP's low molecular size, Mg2+ dependency and catalytic preference for phosphoanhydride bonds are also features of other MutT-type proteins. Because overlapping substrate specificity is a feature of this class of proteins, our data provide new directions for future studies of higher inositol phosphates.
Safrany
S T
ST
Inositide Signaling Group, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, PO Box 12233, NC 27709, USA.
Caffrey
J J
JJ
Yang
X
X
Bembenek
M E
ME
Moyer
M B
MB
Burkhart
W A
WA
Shears
S B
SB
D017766:Acid Anhydride Hydrolases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D029968:Escherichia coli Proteins; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011755:Pyrophosphatases; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D001426:Bacterial Proteins; D018076:DNA, Complementary; D029968:Escherichia coli Proteins; D007295:Inositol Phosphates; D010744:Phosphoric Monoester Hydrolases; D017766:Acid Anhydride Hydrolases; D011755:Pyrophosphatases; C116368:diphosphoinositol polyphosphate phosphohydrolase; C052211:mutT protein, E coli