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Effectory site in Escherichia coli inorganic pyrophosphatase is revealed upon mutation at the intertrimeric interface
Tatyana S Sitnik1, Julia P Vainonen, Elena V Rodina
1Chemistry Department, Moscow State University, Leninskie Gory, 119992 GSP-2, Moscow, Russia.
Abstract:
Escherichia coli inorganic pyrophosphatase (E-PPase) is a homohexamer formed from two trimers related by a two-fold axis. The residue Asp26 participates in intertrimeric contacts. Kinetics of MgPPi hydrolysis by a mutant Asp26Ala E-PPase is found to not obey Michaelis-Menten equation but can be described within the scheme of activation of hydrolysis by a free PPi binding at an effectory subsite. Existence of such a subsite is confirmed by the finding that the free form of methylenediphosphonate activates MgPPi hydrolysis though its magnesium complex is a competitive inhibitor. The Asp26Ala variant is the first example of hexameric E-PPase demonstrated to have an activatory subsite.