epimereras

Epimereras, commonly referred to in English as epimerases, are enzymes that catalyze epimerization, the reversible inversion of configuration at a single stereogenic center in a molecule. As members of the isomerase superfamily, epimerases act on a variety of substrates, with many examples devoted to carbohydrates and their derivatives, including nucleotide-activated sugars used in polysaccharide and glycoprotein biosynthesis.

Epimereras can operate through different catalytic strategies. Some are NAD+-dependent, especially those acting on sugar nucleotides, where the reaction proceeds by oxidation of the target carbon, formation of a transient ketone, and re-reduction to the inverted configuration. Others function without redox changes, employing acid-base catalysis to invert stereochemistry while maintaining oxidation state. The diversity of mechanisms reflects multiple evolutionary origins and substrate preferences.

These enzymes are distributed across bacteria, archaea, plants, and animals, and can be found in the cytosol, organelles, or associated with membranes. They often play essential roles in metabolism and biosynthesis, including the production of cell-wall components such as lipopolysaccharides and teichoic acids, and in the recycling and remodeling of sugar nucleotides used for glycosylation and polysaccharide assembly. In some systems, epimereras participate in pathogen virulence or antibiotic resistance by shaping surface glycans.

Applications and relevance include their use in the biocatalytic synthesis of rare sugars for pharmaceuticals and in metabolic engineering to alter intracellular pools of nucleotide sugars. Structural studies reveal conserved motifs across families, alongside considerable variation in cofactor requirements and substrate scope, underscoring the broad functional diversity of epimereras.

See also: isomerase, epimer, carbohydrate metabolism, UDP-sugars.