title: Kinetics, substrate specificity, and stereospecificity of two new protein tyrosine phosphatase-like inositol polyphosphatases from Selenomonas lacticifex.
abstract: Inositol polyphosphatases (IPPases) play an important role in the metabolism of inositol polyphosphates, a class of molecules involved in signal transduction. Here we characterize 2 new protein tyrosine phosphatase-like IPPases (PhyAsl and PhyBsl) cloned from Selenomonas lacticifex that can hydrolyze myo-inositol hexakisphosphate (InsP6) in vitro. To determine their preferred substrates and stereospecificity of InsP6 dephosphorylation, a combination of kinetic and high-performance ion pair chromatography studies were conducted. Despite only 33% amino acid sequence identity between them, both enzymes display strict specificity for IPP substrates and cleave InsP6 primarily at the D-3-phosphate position (>90%). Furthermore, both enzymes predominantly degrade InsP6 to Ins(2)P via identical and very specific routes of dephosphorylation (3,4,5,6,1). Despite these similarities, PhylAsl is shown to have a slight kinetic preference for the major inositol pentakisphosphate intermediate in its InsP6 hydrolysis pathway, whereas PhyBsl displays a unique and substantial preference for an inositol tetrakisphosphate intermediate.
authors.affiliation: Department of Biological Sciences, University of Lethbridge, Lethbridge, Canada.
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Puhl
authors.forename: Ralf
authors.initials: R
authors.lastname: Greiner
authors.forename: L Brent
authors.initials: LB
authors.lastname: Selinger