5EQ8

Crystal structure of Medicago truncatula Histidinol-Phosphate Phosphatase (MtHPP) in complex with L-histidinol

Summary for 5EQ8

• Entry DOI: 10.2210/pdb5eq8/pdb
• Related: 5EQ7 5EQ9 5EQA
• Descriptor: Inositol monophosphatase, L-histidinol, CHLORIDE ION, ... (4 entities in total)
• Functional Keywords: histidine biosynthesis, metabolic pathways, dimer, plant, biosynthetic protein
• Biological source: Medicago truncatula (Barrel medic)
• Total number of polymer chains: 1
• Total formula weight: 30599.94

Authors

Ruszkowski, M.,Dauter, Z. (deposition date: 2015-11-12, release date: 2016-03-30, Last modification date: 2016-06-01)

Primary citation

Ruszkowski, M.,Dauter, Z.
Structural Studies of Medicago truncatula Histidinol Phosphate Phosphatase from Inositol Monophosphatase Superfamily Reveal Details of Penultimate Step of Histidine Biosynthesis in Plants.
J.Biol.Chem., 291:9960-9973, 2016

PubMed Abstract: The penultimate enzyme in the histidine biosynthetic pathway catalyzes dephosphorylation of l-histidinol 1-phosphate (HOLP) into l-histidinol. 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 an HPP enzyme from a model legume, Medicago truncatula (MtHPP) was based on the 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, the 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 Lys(158) and Cys(245) residues. Four high resolution crystal structures, namely complexes with HOLP (substrate), l-histidinol (product), and PO4 (3-) (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 Mg(2+) cations, is catalyzed mainly by amino acid residues from the N-terminal domain. The C-terminal domain, sharing little identity with IMPases, is responsible for the substrate specificity (i.e. allows the enzyme to distinguish between HOLP and d-myo-inositol-1-phosphate). Structural features, mainly the presence of a conserved Asp(246), allow MtHPP to bind HOLP specifically.

PubMed: 26994138
DOI: 10.1074/jbc.M115.708727

Experimental method

X-RAY DIFFRACTION (1.3 Å)