RESUMEN

Mammalian dihydrofolate reductases (DHFRs) catalyze the reduction of folate more efficiently than the equivalent bacterial enzymes do, despite typically having similar efficiencies for the reduction of their natural substrate, dihydrofolate. In contrast, we show here that DHFR from the hyperthermophilic bacterium Thermotoga maritima can catalyze reduction of folate to tetrahydrofolate with an efficiency similar to that of reduction of dihydrofolate under saturating conditions. Nuclear magnetic resonance and mass spectrometry experiments showed no evidence of the production of free dihydrofolate during either the EcDHFR- or TmDHFR-catalyzed reductions of folate, suggesting that both enzymes perform the two reduction steps without release of the partially reduced substrate. Our results imply that the reaction proceeds more efficiently in TmDHFR than in EcDHFR because the more open active site of TmDHFR facilitates protonation of folate. Because T. maritima lives under extreme conditions where tetrahydrofolate is particularly prone to oxidation, this ability to salvage folate may impart an advantage to the bacterium by minimizing the squandering of a valuable cofactor.

Asunto(s)

Proteínas Bacterianas/química , Ácido Fólico/química , Protones , Tetrahidrofolato Deshidrogenasa/química , Tetrahidrofolatos/química , Thermotoga maritima/enzimología , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Dominio Catalítico , Escherichia coli/química , Escherichia coli/enzimología , Escherichia coli/genética , Ácido Fólico/metabolismo , Expresión Génica , Concentración de Iones de Hidrógeno , Cinética , NADP/química , NADP/metabolismo , Oxidación-Reducción , Pliegue de Proteína , Estructura Secundaria de Proteína , Especificidad de la Especie , Temperatura , Tetrahidrofolato Deshidrogenasa/genética , Tetrahidrofolato Deshidrogenasa/metabolismo , Tetrahidrofolatos/metabolismo , Termodinámica , Thermotoga maritima/química , Thermotoga maritima/genética