Recommended nomenclature for five mammalian carboxylesterase gene families: human, mouse, and rat genes and proteins

Mammalian carboxylesterase (CES or Ces) genes encode enzymes that participate in xenobiotic, drug, and lipid metabolism in the body and are members of at least five gene families. Tandem duplications have added more genes for some families, particularly for mouse and rat genomes, which has caused confusion in naming rodent Ces genes. This article describes a new nomenclature system for human, mouse, and rat carboxylesterase genes that identifies homolog gene families and allocates a unique name for each gene. The guidelines of human, mouse, and rat gene nomenclature committees were followed and “CES” (human) and “Ces” (mouse and rat) root symbols were used followed by the family number (e.g., human CES1). Where multiple genes were identified for a family or where a clash occurred with an existing gene name, a letter was added (e.g., human CES4A; mouse and rat Ces1a) that reflected gene relatedness among rodent species (e.g., mouse and rat Ces1a). Pseudogenes were named by adding “P” and a number to the human gene name (e.g., human CES1P1) or by using a new letter followed by ps for mouse and rat Ces pseudogenes (e.g., Ces2d-ps). Gene transcript isoforms were named by adding the GenBank accession ID to the gene symbol (e.g., human CES1_AB119995 or mouse Ces1e_BC019208). This nomenclature improves our understanding of human, mouse, and rat CES/Ces gene families and facilitates research into the structure, function, and evolution of these gene families. It also serves as a model for naming CES genes from other mammalian species

Structure and Catalytic Properties of Carboxylesterase Isozymes Involved in Metabolic Activation of Prodrugs

Mammalian carboxylesterases (CESs) comprise a multigene family whose geneproducts play important roles in biotransformation of ester- or amide-type prodrugs. Theyare members of an α,β-hydrolase-fold family and are found in various mammals. It has beensuggested that CESs can be classified into five major groups denominated CES1-CES5,according to the homology of the amino acid sequence, and the majority of CESs that havebeen identified belong to the CES1 or CES2 family. The substrate specificities of CES1 andCES2 are significantly different. The CES1 isozyme mainly hydrolyzes a substrate with asmall alcohol group and large acyl group, but its wide active pocket sometimes allows it toact on structurally distinct compounds of either a large or small alcohol moiety. In contrast,the CES2 isozyme recognizes a substrate with a large alcohol group and small acyl group,and its substrate specificity may be restricted by the capability of acyl-enzyme conjugateformation due to the presence of conformational interference in the active pocket. Sincepharmacokinetic and pharmacological data for prodrugs obtained from preclinicalexperiments using various animals are generally used as references for human studies, it isimportant to clarify the biochemical properties of CES isozymes. Further experimentationfor an understanding of detailed substrate specificity of prodrugs for CES isozymes and itshydrolysates will help us to design the ideal prodrugs