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Sulfolobus acidocaldarius inorganic pyrophosphatase: Structure, thermostability, and effect of metal ion in an archael pyrophosphatase
Author(s) -
Leppänen VeliMatti,
Nummelin Heli,
Hansen Thomas,
Lahti Reijo,
Schäfer Günter,
Goldman Adrian
Publication year - 1999
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.8.6.1218
Subject(s) - inorganic pyrophosphatase , thermostability , sulfolobus acidocaldarius , pyrophosphatase , thermus thermophilus , pyrophosphatases , chemistry , crystallography , thermophile , stereochemistry , monomer , biochemistry , pyrophosphate , enzyme , escherichia coli , organic chemistry , archaea , gene , polymer
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 Å. S‐PPase is a D 3 homohexameric protein with one Mg 2+ 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 Mg 2+ while only Asp65 and Asp102 do in S‐PPase, and the Mg 2+ moves by 0.7 Å. 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 Å/Cα. 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.