5eq8

Publication Abstract from PubMed

The penultimate enzyme in the histidine biosynthetic pathway catalyzes dephosphorylation of L-histidinol 1-phosphate (HOLP) into L-histidinol (HOL). The recently discovered in Arabidopsis thaliana plant-type histidinol-phosphate phosphatase (HPP) shares no homology with the two other HPP superfamilies known previously in prokaryotes, and resembles myo-inositol monophosphatases (IMPases). In this work, identification of a HPP enzyme from a model legume, Medicago truncatula (MtHPP) was based on highest sequence identity to A. thaliana enzyme. Biochemical assays confirmed that MtHPP was able to cleave inorganic phosphate from HOLP but not from D-myo-inositol-1-phosphate (IMP), main substrate of IMPases. Dimers of MtHPP, determined by size-exclusion chromatography, in the presence of CO2 or formaldehyde form mutual, methylene-bridged cross-links between Lys158 and Cys245 residues. Four high resolution crystal structures, namely complexes with: HOLP (substrate), HOL (product), PO43- (by-product), as well as the structure showing the cross-linking between two MtHPP molecules, provide detailed structural information on the enzyme. Based on the crystal structures, the enzymatic reaction mechanism of IMPases is accustomed to fit the data for MtHPP. The enzymatic reaction, which requires Mg2+ cations, is catalyzed mainly by amino acid residues from the N-terminal domain. C-terminal domain, sharing little identity to IMPases, is responsible for the substrate specificity, that is, allows the enzyme to distinguish between HOLP and IMP. Structural features, mainly the presence of a conserved Asp246, allow MtHPP to bind HOLP specifically.

Structural studies of Medicago truncatula histidinol-phosphate phosphatase from inositol monophosphatase superfamily reveal details of penultimate step of histidine biosynthesis in plants.,Ruszkowski M, Dauter Z J Biol Chem. 2016 Mar 18. pii: jbc.M115.708727. PMID:26994138^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.