Changes in E. coli Inorganic Pyrophosphatase Structure Induced by Binding of Metal Activators

S. M. Avaeva^1*, E. V. Rodina¹, N. N. Vorobyeva², S. A. Kurilova¹, T. I. Nazarova¹, V. A. Sklyankina², V. Yu. Oganessyan³, 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.crystal.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 E. coli inorganic pyrophosphatase (PPase) and its complexes with Mn²⁺ in a high affinity site and with Mg²⁺ in high and low affinity sites determined by authors in 1994-1996 at 1.9-2.2 Å resolution are compared. Metal ion binding initiates the shifts of alpha-carbon atoms and of functional groups and rearrangement of non-covalent interaction system of hexameric enzyme molecule. As a result, the apoPPase with six equal subunits turns after Mg²⁺ binding into the structure with three types of subunits distinguished by structure and occupance of the low affinity Mg²⁺ site. Induced asymmetry reflects the subunit interactions and cooperativity between Mg²⁺ binding sites. These molecular rearrangements are structural basis to account for special features of the enzyme behavior and to propose one of the pathways for enzymatic activity regulation of constitutive PPases in vivo.

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KEY WORDS: inorganic pyrophosphatase, Escherichia coli, apoenzyme, complex with Mn²⁺, complex with Mg²⁺, three-dimensional structure

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