1qt3

OverviewOverview

In contrast to hen egg-white lysozyme, which retains the, beta-configuration of the substrate in the product, T4 lysozyme (T4L) is, an inverting glycosidase. The substitution Thr-26 --> His, however, converts T4L from an inverting to a retaining enzyme. It is shown here, that the Thr-26 --> His mutant is also a transglycosidase. Indeed, the, transglycosylation reaction can be more effective than hydrolysis. In, contrast, wild-type T4L has no detectable transglycosidase activity. The, results support the prior hypothesis that catalysis by the Thr-26 --> His, mutant proceeds via a covalent intermediate. Further mutations (Glu-11 -->, His, Asp-20 --> Cys) of the T26H mutant lysozyme indicate that the, catalytic mechanism of this mutant requires Glu-11 as a general acid but, Asp-20 is not essential. The results help provide an overall, rationalization for the activity of glycosidases, in which a highly, conserved acid group (Glu-11 in T4L, Glu-35 in hen egg-white lysozyme) on, the beta-side of the substrate acts as a proton donor, whereas alterations, in the placement and chemical identity of residues on the alpha-side of, the substrate can lead to catalysis with or without retention of the, configuration, to transglycosidase activity, or to the formation of a, stable enzyme-substrate adduct.

About this StructureAbout this Structure

1QT3 is a Single protein structure of sequence from Bacteriophage t4 with CL and HED as ligands. Active as Lysozyme, with EC number 3.2.1.17 Full crystallographic information is available from OCA.

ReferenceReference

Structural basis of the conversion of T4 lysozyme into a transglycosidase by reengineering the active site., Kuroki R, Weaver LH, Matthews BW, Proc Natl Acad Sci U S A. 1999 Aug 3;96(16):8949-54. PMID:10430876

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