Single amino acid changes outside the active site significantly affect activity of glutathione S-transferases

Glutathione S-transferases (GSTs: E.C. 2.5.1.18) are a multigene family of multifunctional dimeric proteins that play a central role in detoxication. Four allelic forms of the mosquito Anopheles dirus GST, adGST1-1, were clon ed, expressed and characterized. The one or two amino acid changes in each allelic form was shown to confer different kinetic properties. Based on an available crystal structure, several of the residue changes were not in the putative substrate-binding pocket. Modeling showed that these insect Delta class GSTs also possess a hydrophobic surface pocket reported for Alpha, M u and Pi class GSTs. The atom movement after replacement and minimization s howed an average atom movement of about 0.1 Angstrom for the 0 to 25 Angstr om distance from the alpha carbon of the single replaced residue. This does not appear to be a significant movement in a static modeled protein struct ure. However, 200-500 atoms were involved with movements greater than 0.2 A ngstrom. Dynamics simulations were performed to study the effects this phen omenon would exert on the accessible conformations. The data show that resi dues affecting nearby responsive regions of tertiary structure can modulate enzyme specificities, possibly through regulating attainable configuration s of the protein. (C) 2001 Elsevier Science Ltd. All rights reserved.