In wild-type glutathione reductase from Escherichia coli residues Val421 and Ala422 are located in an alpha-helix in a densely packed and hydrophobic region of the dimer interface, with their side chains packed against those of residues Ala422′ and Val421′ in the second subunit. A series of mutant glutathione reductases was constructed in which the identities of the residues at positions 421 and 422 were changed. Mutations were designed so as to present like charges (mutants Val421-->Glu:Ala422-->Glu and Val421-->Lys:Ala422-->Lys) or opposite charges (mutant Val421-->Lys:Ala422-->Glu) across the dimer interface to assess the role of electrostatic interactions in dimer stability. A fourth mutant (Val421-->His:Ala422-->His) was also constructed to investigate the effects of introducing a potentially protonatable bulky side chain into a crowded region of the dimer interface. In all cases, an active dimeric enzyme was found to be assembled but each mutant protein was thermally destabilized. A detailed steady-state kinetic analysis indicated that each mutant enzyme no longer displayed the Ping Pong kinetic behaviour associated with the wild-type enzyme but exhibited what was best described as a random bireactant ternary complex mechanism. This leads, depending on the chosen substrate concentration, to apparent sigmoidal, hyperbolic or complex kinetic behaviour. These experiments, together with others reported previously, indicate that simple mutagenic changes in regions distant from the active site can lead to dramatic switches in steady-state kinetic mechanism.
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December 1995
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Research Article|
December 01 1995
Altering kinetic mechanism and enzyme stability by mutagenesis of the dimer interface of glutathione reductase Available to Purchase
A Bashir;
A Bashir
1Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, U.K.
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R N Perham;
R N Perham
1Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, U.K.
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N S Scrutton;
N S Scrutton
1Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, U.K.
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A Berry
A Berry
1Cambridge Centre for Molecular Recognition, Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, U.K.
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1995 The Biochemical Society, London
1995
Biochem J (1995) 312 (2): 527–533.
Citation
A Bashir, R N Perham, N S Scrutton, A Berry; Altering kinetic mechanism and enzyme stability by mutagenesis of the dimer interface of glutathione reductase. Biochem J 1 December 1995; 312 (2): 527–533. doi: https://doi.org/10.1042/bj3120527
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