This family was extracted from the previous Carboxylesterase COesterase family. This family corresponds to the Carbohydrate Esterase family CE10 in CAZy - Carbohydrate-Active enZYmes database (CE_10).
The evolution of organismal diversity among the Metazoa is dependent on the proliferation of genes and diversification of functions in multigene families. Here we analyse these processes for one highly successful family, the carboxyl/cholinesterases. One key to the expansion of the functional niche of this group of enzymes is associated with versatile substrate binding and catalytic machinery. Qualitatively new functions can be obtained by substitution of one or a very few amino acids. This crudely adapted new functionality is then refined rapidly by a pulse of change elsewhere in the molecule; in one case about 13% amino acid divergence occurred in 5-10 million years. Furthermore, we postulate that the versatility of the substrate binding motifs underpins the recruitment of several family members to additional noncatalytic signal transduction functions.
Comparisons among the primary sequences of five cloned eukaryotic esterases reveal two distinct lineages, neither bearing any significant overall sequence similarity to the functionally related serine protease multigene family. We have not eliminated the possibility that the esterases may have residual conformational similarities to the serine proteases. However, our profile analysis and analyses of the predicted conformations of the esterases reveal little similarity to the serine proteases. Four of the esterase proteins share 27%-53% overall sequence similarity and evidence of a catalytic mechanism involving the same Arg-Asp-Ser or His-Asp-Ser charge relay. We propose that these four esterases, three of them cholinesterases, form part of a multigene family essentially separate from the serine proteases.
