title: Sulfolobus acidocaldarius inorganic pyrophosphatase: structure, thermostability, and effect of metal ion in an archael pyrophosphatase.
abstract: The first crystal structure of an inorganic pyrophosphatase (S-PPase) from an archaebacterium, the thermophile Sulfolobus acidocaldarius, has been solved by molecular replacement and refined to an R-factor of 19.7% at 2.7 A. S-PPase is a D3 homohexameric protein with one Mg2+ per active site in a position similar to, but not identical with, the first activating metal in mesophilic pyrophosphatases (PPase). In mesophilic PPases, Asp65, Asp70, and Asp102 coordinate the Mg2+, while only Asp65 and Asp102 do in S-PPase, and the Mg2+ moves by 0.7 A. S-PPase may therefore be deactivated at low temperature by mispositioning a key metal ion. The monomer S-PPase structure is very similar to that of Thermus thermophilus (T-PPase) and Escherichia coli (E-PPase), root-mean-square deviations around 1 A/Calpha. But the hexamer structures of S- and T-PPase are more tightly packed and more similar to each other than they are to that of E-PPase, as shown by the increase in surface area buried upon oligomerization. In T-PPase, Arg116 creates an interlocking ionic network to both twofold and threefold related monomers; S-PPase has hydrophilic interactions to threefold related monomers absent in both E- and T-PPase. In addition, the thermostable PPases have about 7% more hydrogen bonds per monomer than E-PPase, and, especially in S-PPase, additional ionic interactions anchor the C-terminus to the rest of the protein. Thermostability in PPases is thus due to subtle improvements in both monomer and oligomer interactions.
authors.affiliation: Department of Biochemistry and Food Technology, University of Turku, Finland.
authors.forename: V M
authors.initials: VM
authors.lastname: Leppänen
authors.forename: H
authors.initials: H
authors.lastname: Nummelin
authors.forename: T
authors.initials: T
authors.lastname: Hansen
authors.forename: R
authors.initials: R
authors.lastname: Lahti
authors.forename: G
authors.initials: G
authors.lastname: Schäfer
authors.forename: A
authors.initials: A
authors.lastname: Goldman
mesh_terms: D000595:Amino Acid Sequence; D004795:Enzyme Stability; D043564:Inorganic Pyrophosphatase; D008670:Metals / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011755:Pyrophosphatases / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016945:Sulfolobus acidocaldarius / Q000201:enzymology*
chemical_list: D008670:Metals; D011755:Pyrophosphatases; D043564:Inorganic Pyrophosphatase