Identification of a cytoplasmic manganese superoxide dismutase (cMnSOD) in the red swamp crawfish, Procambarus clarkii: cDNA cloning and tissue expression.

A cytoplasmic manganese superoxide dismutase (cMnSOD) cDNA was cloned from the hepatopancreas of the red swamp crawfish, Procambarus clarkii. An initial cDNA fragment was identified by using degenerate primers, and the complete sequence was obtained by using RACE methodology. The full sequence comprises 1140 bp, with an open reading frame of 858 bp encoding a protein of 286 amino acids. Sequence analysis showed that this protein is highly homologous to previously obtained crustacean cMnSODs. Phylogenetic analysis clusters it with all known cMnSODs and in a group distinct from mitochondrial MnSODs. cMnSOD transcripts were detected in the gills, tail muscle, green glands, and hepatopancreas. The data provide additional evidence for the hypothesis that cMnSOD replaced CuZnSOD in crustaceans that use haemocyanin as the respiratory pigment.