An Examination of the Role of Asp-177 in the His-Asp Catalytic Dyad of Leuconostoc Mesenteroides Glucose 6-Phosphate Dehydrogenase: X-Ray Structure and Ph Dependence of Kinetic Parameters of the D177N Mutant EnzymeCosgrove, M.S., Gover, S., Naylor, C.E., Vandeputte-Rutten, L., Adams, M.J., Levy, H.R.
(2000) Biochemistry 39: 15002
- PubMed: 11106478
- Primary Citation of Related Structures:  1E77, 1E7M
- Also Cited By: 1H93, 1H94, 1H9A, 1H9B
- PubMed Abstract:
- The Three-Dimensional Structure of Glucose 6-Phosphate Dehydrogenase from Leuconostoc Mesenteroides Refined at 2 Angstroms Resolution
Rowland, P.,Basak, A.K.,Gover, S.,Levy, H.R.,Adams, M.J.
(1994) Structure 2: 1073
- On the Mechanism of the Reaction Catalysed by Glucose 6-Phosphate Dehydrogenase
Cosgrove, M.S.,Naylor, C.,Paludin, S.,Adams, M.J.,Levy, H.R.
(1998) Biochemistry 37: 2759
The role of Asp-177 in the His-Asp catalytic dyad of glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides has been investigated by a structural and functional characterization of the D177N mutant enzyme. Its three-dimensional structure ha ...
The role of Asp-177 in the His-Asp catalytic dyad of glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides has been investigated by a structural and functional characterization of the D177N mutant enzyme. Its three-dimensional structure has been determined by X-ray cryocrystallography in the presence of NAD(+) and in the presence of glucose 6-phosphate plus NADPH. The structure of a glucose 6-phosphate complex of a mutant (Q365C) with normal enzyme activity has also been determined and substrate binding compared. To understand the effect of Asp-177 on the ionization properties of the catalytic base His-240, the pH dependence of kinetic parameters has been determined for the D177N mutant and compared to that of the wild-type enzyme. The structures give details of glucose 6-phosphate binding and show that replacement of the Asp-177 of the catalytic dyad with asparagine does not affect the overall structure of glucose 6-phosphate dehydrogenase. Additionally, the evidence suggests that the productive tautomer of His-240 in the D177N mutant enzyme is stabilized by a hydrogen bond with Asn-177; hence, the mutation does not affect tautomer stabilization. We conclude, therefore, that the absence of a negatively charged aspartate at 177 accounts for the decrease in catalytic activity at pH 7.8. Structural analysis suggests that the pH dependence of the kinetic parameters of D177N glucose 6-phosphate dehydrogenase results from an ionized water molecule replacing the missing negative charge of the mutated Asp-177 at high pH. Glucose 6-phosphate binding orders and orients His-178 in the D177N-glucose 6-phosphate-NADPH ternary complex and appears to be necessary to form this water-binding site.
Department of Biology, Syracuse University, Syracuse, New York 13244, USA.