title: IP6K structure and the molecular determinants of catalytic specificity in an inositol phosphate kinase family.
abstract: Inositol trisphosphate kinases (IP3Ks) and inositol hexakisphosphate kinases (IP6Ks) each regulate specialized signalling activities by phosphorylating either InsP3 or InsP6 respectively. The molecular basis for these different kinase activities can be illuminated by a structural description of IP6K. Here we describe the crystal structure of an Entamoeba histolytica hybrid IP6K/IP3K, an enzymatic parallel to a 'living fossil'. Through molecular modelling and mutagenesis, we extrapolated our findings to human IP6K2, which retains vestigial IP3K activity. Two structural elements, an α-helical pair and a rare, two-turn 310 helix, together forge a substrate-binding pocket with an open clamshell geometry. InsP6 forms substantial contacts with both structural elements. Relative to InsP6, enzyme-bound InsP3 rotates 55° closer to the α-helices, which provide most of the protein's interactions with InsP3. These data reveal the molecular determinants of IP6K activity, and suggest an unusual evolutionary trajectory for a primordial kinase that could have favored efficient bifunctionality, before propagation of separate IP3Ks and IP6Ks.
authors: Inositol Signaling Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, NC 27709, USA.
authors: Huanchen
authors: H
authors: Wang
authors: Nuclear Magnetic Resonance Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, NC 27709, USA.
authors: Eugene F
authors: EF
authors: DeRose
authors: Nuclear Magnetic Resonance Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, NC 27709, USA.
authors: Robert E
authors: RE
authors: London
authors: Inositol Signaling Group, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, NC 27709, USA.
authors: Stephen B
authors: SB
authors: Shears
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004748:Entamoeba histolytica / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D007295:Inositol Phosphates / Q000737:chemistry / Q000378:metabolism*; D005810:Multigene Family; D017856:Phosphotransferases (Phosphate Group Acceptor) / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012680:Sensitivity and Specificity
chemical_list: D007295:Inositol Phosphates; D015800:Protozoan Proteins; D000255:Adenosine Triphosphate; D017856:Phosphotransferases (Phosphate Group Acceptor); C099438:inositol hexakisphosphate kinase