Characterization of the hydrophobic substrate-binding site of the bacterial beta class glutathione transferase from Proteus mirabilis.

Since their discovery, bacterial glutathione (GSH) trans- ferases have been characterized in terms of their ability to catalyse a variety of different reactions on a large set of toxic molecules of xenobiotic or endobiotic origin. Furthermore the contribution of different residues in the GSH-binding site to GSH activation has been extensively investigated. Little is known, however, about the contri- bution to catalysis and overall stability of single residues shaping the hydrophobic co-substrate binding site (H- site). Here we tackle this problem by site-directed muta- genesis of residues facing the H-site in the bacterial beta class GSH transferase from Proteus mirabilis. We investi- gate the behaviour of these mutants under a variety of conditions and analyse their activity against several co- substrates, representative of the different reactions cata- lyzed by bacterial GSH transferases. Our work shows that mutations at the H-site can be used to modulate activity at the level of the different catalytic mechanisms operating on the chosen substrates, each mutation showing a different fingerprint. This work paves the way for future studies aimed at improving the catalytic prop- erties of beta class GSH transferases against selected sub- strates for bioremediation purposes.