Dissociation of hexameric Escherichia coli inorganic pyrophosphatase into trimers on His-136->Gln or His-140->Gln substitution and its effect on enzyme catalytic properties

A1 Originalartikel i en vetenskaplig tidskrift (referentgranskad)


Interna författare/redaktörer


Publikationens författare: Baykov AA, Dudarenkov VY, Käpylä J, Salminen T, Hyytiä T, Kasho VN, Husgafvel S, Cooperman BS, Goldman A, Lahti R
Förläggare: AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Publiceringsår: 1995
Tidskrift: Journal of Biological Chemistry
Tidskriftsakronym: J BIOL CHEM
Volym: 270
Artikelns första sida, sidnummer: 30804
Artikelns sista sida, sidnummer: 30812
Antal sidor: 9
ISSN: 0021-9258


Abstrakt

Each of the five histidines in Escherichia coli inorganic pyrophosphatase (PPase) was replaced in turn by glutamine. Significant changes in protein structure and activity were observed in the H136Q and H140Q variants only. In contrast to wild-type PPase, which is hexameric, these variants can be dissociated into trimers by dilution, as shown by analytical ultracentrifugation and cross-linking. Mg2+ and substrate stabilize the hexameric forms of both variants. The hexameric H136Q- and H140Q-PPases have the same binding affinities for magnesium ion as wild-type, but their hydrolytic activities under optimal conditions are, respectively, 225 and 110% of wild-type PPase, and their synthetic activities, 340 and 140%. The increased activity of hexameric H136Q-PPase results from an increase in the rate constants governing most of the catalytic steps in both directions. Dissociation of the hexameric H136Q and H140Q variants into trimers does not affect the catalytic constants for PPi hydrolysis between pH 6 and 9 but drastically decreases their affinities for Mg2PPi and Mg2+. These results prove that His-136 and His-140 are key residues in the dimer interface and show that hexamer formation improves the substrate binding characteristics of the active site.

Senast uppdaterad 2019-20-11 vid 04:03