Protein-ribofuranosyl interactions activate orotidine 5′-monophosphate decarboxylase for catalysis
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Universidade Federal de Minas Gerais
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The role of a global, substrate-driven, enzyme conformational change in enabling the extraordinarily large rate acceleration for orotidine 5′-monophosphate decarboxylase (OMPDC)-catalyzed decarboxylation of orotidine 5′-monophosphate(OMP) is examined in experiments that focus on the interactions between OMPDC and the ribosyl hydroxyl groups ofOMP. TheD37 and T100′side chains of OMPDC interact, respectively, with the C-3′and C-2′hydroxyl groups of enzyme-boundOMP.D37G and T100′A substitutions result in 1.4 kcal/mol increases in the activation barrier ΔG⧧for catalysis of decarboxylation of thephosphodianion-truncated substrate 1-(β-D-erythrofuranosyl) orotic acid (EO) but result in larger 2.1−2.9 kcal/mol increases in ΔG⧧for decarboxylation of OMPand for phosphite dianion-activated decarboxylation of EO. This shows that these substitutions reduce transition-state stabilization by the Q215, Y217, and R235 side chains at the dianion binding site. The D37G and T100′A substitutions result in <1.0 kcal/mol increases in ΔG⧧ for activation of OMPDC-catalyzed decarboxylation of the phosphoribofuranosyl-truncated substrate FO by phosphite dianions. Experiments to probe the effect of D37 and T100′substitutions on the kinetic parameters for D-glycerol 3-phosphate and D-erythritol 4-phosphate activators of OMPDC-catalyzed decarboxylation of FO show that ΔG⧧for sugar phosphate-activated reactions is increased byca.2.5 kcal/mol for each −OH interaction eliminated by D37G or T100′A substitutions. We conclude that the interactions between the D37 and T100′side chainsand ribosyl or ribosyl-like hydroxyl groups are utilized to activate OMPDC for catalysis of decarboxylation of OMP, EO, and FO.
Abstract
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Proteinas, Análise enzimática, Cinética de enzimas, Mecanismos de reações orgânicas, Reações químicas, Bioquímica
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Chemical reactions, Kinetic parameters, Organic reactions, Peptides and proteins, Stabilization
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https://pubs.acs.org/doi/10.1021/acs.biochem.1c00589