Glutathione S‐transferases: Amino acid sequence comparison, classification and phylogenetic relationship

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Abstract
We have assembled a data base for 71 full length and near‐full length amino acid sequences of glutathione S‐transferases from various vertebrate and invertebrate eukaryotic and prokaryotic species. This database was used as input for multiple sequence alignment and a dendrogram was established representing the classification and phylogenetic relationship of the glutathione S‐transferase supergene family. The glutathione S‐transferase sequences were grouped into six classes; five of them are established classes identified as alpha, mu, pi, theta and microsomal. The lens S‐crystallin amino acid sequences from squid and octopus were grouped into a new class termed sigma. A hypothesis of the origin and evolution of glutathione S‐transferases is proposed. Glutathione S‐transferases are present in primitive prokaryotic organisms and the ancestral gene for glutathione S‐transferase probably was a member of the theta class. Gene duplication followed by diversification has led to the multiplicity of glutathione S‐transferases known today which comprise almost one hundred individual isozymes.