RESUMEN
The crystal structure of recombinant murine liver cytosolic epoxide hydrolase (EC 3.3.2.3) has been determined at 2.8-A resolution. The binding of a nanomolar affinity inhibitor confirms the active site location in the C-terminal domain; this domain is similar to that of haloalkane dehalogenase and shares the alpha/beta hydrolase fold. A structure-based mechanism is proposed that illuminates the unique chemical strategy for the activation of endogenous and man-made epoxide substrates for hydrolysis and detoxification. Surprisingly, a vestigial active site is found in the N-terminal domain similar to that of another enzyme of halocarbon metabolism, haloacid dehalogenase. Although the vestigial active site does not participate in epoxide hydrolysis, the vestigial domain plays a critical structural role by stabilizing the dimer in a distinctive domain-swapped architecture. Given the genetic and structural relationships among these enzymes of xenobiotic metabolism, a structure-based evolutionary sequence is postulated.
Asunto(s)
Carcinógenos/farmacocinética , Epóxido Hidrolasas/química , Epóxido Hidrolasas/genética , Epóxido Hidrolasas/farmacocinética , Inactivación Metabólica , Hígado/enzimología , Mutágenos/farmacocinética , Animales , Cristalografía por Rayos X , Dimerización , Hidrolasas/química , Hidrólisis , Ratones , Modelos Químicos , Modelos Moleculares , Datos de Secuencia Molecular , Conformación Proteica , Estructura Terciaria de Proteína , Proteínas Recombinantes/química , Xenobióticos/metabolismoRESUMEN
Over the past two decades, pharmacokinetic data have clearly demonstrated that development can markedly influence the absorption, distribution, excretion, and metabolism of xenobiotics. With respect to many of the processes that govern drug metabolism, the underlying pharmacogenetic determinants that may control either the affinity or the capacity of a drug or toxicant substrate for the enzymes responsible for its biotransformation appear to be altered as a function of development by mechanisms that are, for the most part, not well defined. Nonetheless, for many xenobiotics, the pharmacogenetic-developmental interface produces a "pattern" for drug metabolism that, when characterized, supports the pharmacokinetic properties (eg, drug clearance) reported for many agents across the pediatric age spectrum. With the exception of a few relatively well-characterized adverse drug effects (eg, toxicity of 6-mercaptopurine in patients with absent thiopurine methyltransferase activity, increased incidence of hepatotoxicity to valproic acid in young infants), the relationship of development and pharmacogenetics to enhanced toxicity risk from xenobiotic exposure is poorly defined. However, failure to adequately appreciate the pharmacokinetic consequences of the pharmacogenetic-developmental interface and to individualize therapy accordingly may lead to a clinically significant risk of drug therapy, namely, over- or underdosing.