Dihydrofolate reductase transition state

Figure 10. The ternary complex of the enzyme dihydrofolate reductase, the substrate and the cofactor during the transition state of the hydride ion transfer. The enzyme backbone atoms are shown alone for clarity and are colored blue. The substrate is shown in yellow and the cofactor is in red. The bond colored in light blue indicates the hydride ion being shared by both the cofactor and the substrate before the transfer to the substrate. Water molecules around the residue pteridine of the substrate and the nicotinamide ring of the cofactor alone are shown and colored in light blue. The yellow spheres represent the sodium ions and the pink spheres the chloride ions.

C. Bystroff, S.J. Oatley, and J. Kraut. 1990. Crystal structures oiEscherichia coli dihydrofolate reductase TheNADP+ holoenzyme and the folate NADP+ ternary complex Substrate binding and a model for the transition state Biochemistry 29 3263-3277. (PubMed)... 

Crystal Structure of Escherichia coli Dihydrofolate Reductase The Binding of NADP+ Holoenzyme and the Eolate NADP+ Ternary Complex. Substrate Binding and a Model for the Transition State, Biochemistry 29, 3263-3277. 

Li, L., Falzone, C. J., Wright, P. E., Benkovig, S. J. (1992) Functional role of a mobile loop of E.coli dihydrofolate reductase in transition-state stabilization, Biochemistry 31, 7826-7833. 

Bystroee, C., Oatley, S. J., Kraut, J. (1990) Crystal structures of Escherichia coli dihydrofolate reductase the NADP-I- holoenzyme and the folate NADP-I- ternary complex. Substrate binding and a model for the transition state. Biochemistry 29, 3263-3277. 

Selected examples of apparent free energies of interaction attributable to single amino acid side chains are summarized for three enzymes, T4 lysozyme, dihydrofolate reductase (DHFR), and tyrosyl-tRNA synthetase (TRS) (see Figs. 1,5, and 12, respectively, for structural information). In each case, the thermodynamic effect of the substitution was quantitated in terms of reduced binding affinity for the substrate or transition state, or reduced thermostability in the case of T4 lysozyme. 

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