Interaction of the catalytic domain of inositol 1,4,5-trisphosphate 3-kinase A with inositol phosphate analogues.
The levels of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] in the cytoplasm are tightly regulated by two enzymes, Ins(1,4,5)P3 3-kinase and type I Ins(1,4,5)P3 5-phosphatase. The catalytic domain of Ins(1,4,5)P3 3-kinase (isoenzymes A, B and C) is restricted to approximately 275 amino acids at the C-terminal end. We were interested in understanding the catalytic mechanism of this key family of enzymes in order to exploit this in inhibitor design. We expressed the catalytic domain of rat Ins(1,4,5)P3 3-kinase A in Escherichia coli as a His- and S-tagged fusion protein. The purified enzyme was used in an Ins(1,4,5)P3 kinase assay to phosphorylate a series of inositol phosphate analogues with three or four phosphate groups. A synthetic route to D-2-deoxy-Ins(1,4,5)P3 was devised. D-2-Deoxy-Ins(1,4,5)P3 and D-3-deoxy-Ins(1,4,6)P3 were potent inhibitors of the enzyme, with IC50 values in the micromolar range. Amongst all analogues tested, only D-2-deoxy-Ins(1,4,5)P3 appears to be a good substrate of the Ins(1,4,5)P3 3-kinase. Therefore, the axial 2-hydroxy group of Ins(1,4,5)P3 is not involved in recognition of the substrate nor does it participate in the phosphorylation mechanism of Ins(1,4,5)P3. In contrast, the equatorial 3-hydroxy function must be present in that configuration for phosphorylation to occur. Our data indicate the importance of the 3-hydroxy function in the mechanism of inositol trisphosphate phosphorylation rather than in substrate binding.
Interdisciplinary Research Institute (IRIBHM), Université Libre de Bruxelles, Campus Erasme, Bldg C, 808 Route de Lennik, 1070 Brussels, Belgium.
Alexandra
A
Poinas
Katrien
K
Backers
Andrew M
AM
Riley
Stephen J
SJ
Mills
Colette
C
Moreau
Barry V L
BV
Potter
Christophe
C
Erneux
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007295:Inositol Phosphates / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry* / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry* / Q000235:genetics; D013329:Structure-Activity Relationship
D007295:Inositol Phosphates; D011994:Recombinant Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase