Enzymatic Synthesis of γ-Glutamyl Dipeptides Catalysed by Mutant E. coli γ-Glutamyltransferases

g-Glutamyltransferases (GGTs) from different sources have been proposed in recent times as biocatalysts for the enzymatic synthesis of naturally occurring g-glutamyl derivatives with flavor-enhancer properties and interesting biological activities. Although the enzymatic approach is considered as a viable alternative to both the troublesome and low-yielding extraction from natural sources and synthesis through peptide chemistry requiring protection/deprotection steps, yields are not completely satisfactory, due to the intervention of GGT-catalysed hydrolysis and autotranspeptidation side-reactions. Here, the design and the use as biocatalyst for preparative purposes of two mutants of E. coli GGT are described. The design of mutants was pursued by docking-guided identification of residues putatively involved in interaction with the acceptor substrate, thus probably representing a first identification of residues constituting the still elusive and poorly characterized acceptor substrate binding site of the enzyme.