title: Crystal structure of the hyperthermophilic inorganic pyrophosphatase from the archaeon Pyrococcus horikoshii.
abstract: A homolog to the eubacteria inorganic pyrophosphatase (PPase, EC 3.6.1.1) was found in the genome of the hyperthermophilic archaeon Pyrococcus horikoshii. This inorganic pyrophosphatase (Pho-PPase) grows optimally at 88 degrees C. To understand the structural basis for the thermostability of Pho-PPase, we have determined the crystal structure to 2.66 A resolution. The crystallographic asymmetric unit contains three monomers related by approximate threefold symmetry, and a hexamer is built up by twofold crystallographic symmetry. The main-chain fold of Pho-PPase is almost identical to that of the known crystal structure of the model from Sulfolobus acidocaldarius. A detailed comparison of the crystal structure of Pho-PPase with related structures from S. acidocaldarius, Thermus thermophilus, and Escherichia coli shows significant differences that may account for the difference in their thermostabilities. A reduction in thermolabile residues, additional aromatic residues, and more intimate association between subunits all contribute to the larger thermophilicity of Pho-PPase. In particular, deletions in two loops surrounding the active site help to stabilize its conformation, while ion-pair networks unique to Pho-PPase are located in the active site and near the C-terminus. The identification of structural features that make PPases more adaptable to extreme temperature should prove helpful for future biotechnology applications.
authors.affiliation: Laboratory of Structural Biology, Tsinghua University and National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China.
authors.forename: Binbin
authors.initials: B
authors.lastname: Liu
authors.forename: Mark
authors.initials: M
authors.lastname: Bartlam
authors.forename: Renjun
authors.initials: R
authors.lastname: Gao
authors.forename: Weihong
authors.initials: W
authors.lastname: Zhou
authors.forename: Hai
authors.initials: H
authors.lastname: Pang
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Liu
authors.forename: Yan
authors.initials: Y
authors.lastname: Feng
authors.forename: Zihe
authors.initials: Z
authors.lastname: Rao
mesh_terms: D000595:Amino Acid Sequence; D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods*; D019281:Dimerization; D004795:Enzyme Stability; D043564:Inorganic Pyrophosphatase / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D043902:Pyrococcus horikoshii / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D013696:Temperature
chemical_list: D043564:Inorganic Pyrophosphatase