Three-Dimensional Structures of Mutant Forms of E. coli Inorganic Pyrophosphatase with Asp-->Asn Single Substitution in Positions 42, 65, 70, and 97

S. M. Avaeva^1*, E. V. Rodina¹, N. N. Vorobyeva², S. A. Kurilova¹, T. I. Nazarova¹, V. A. Sklyankina², V. Yu. Oganessyan³, V. R. Samygina³, and E. H. Harutyunyan³

¹Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3181; E-mail: avaeva@protchem.genebee.msu.su

²School of Chemistry, Lomonosov Moscow State University, Moscow, 119899 Russia

³Shubnikov Institute of Crystallography, Leninskii pr. 59, Moscow, 117333 Russia; fax: (095) 135-1011; E-mail: emil@protein.cryst.msk.ru

^* To whom correspondence should be addressed.

Received October 13, 1997; Revision received December 3, 1997

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The three-dimensional structures of four mutant E. coli inorganic pyrophosphatases (PPases) with single Asp-->Asn substitutions at positions 42, 65, 70, and 97 were solved at 1.95, 2.15, 2.10, and 2.20 Å resolution, respectively. Asp-42-->Asn and Asp-65-->Asn mutant PPases were prepared as complexes with sulfate--a structural analog of phosphate, the product of enzymatic reaction. A comparison of mutant enzymes with native PPases revealed that a single amino acid substitution changes the position of the mutated residue as well as the positions of several functional groups and some parts of a polypeptide chain. These changes are responsible for the fact that mutant PPases differ from the native ones in their catalytic properties. The sulfate binding to the mutant PPase active site causes molecular asymmetry, as shown for the native PPase earlier. The subunit asymmetry is manifested in different positions of sulfate and several functional groups, as well as changes in packing of hexamers in crystals and in cell parameters.

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KEY WORDS: inorganic pyrophosphatase, Escherichia coli, mutant form, aspartic acid, asparagine, complex with sulfate, three-dimensional structure

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