Molecular cloning of a hemopexin-like cDNA from rainbow trout liver

Hemopexin is an abundant heme-binding serum protein synthesized in the liver and for which the sequence is determined only for mammals. Little is known about fish heme-binding proteins. We have cloned a rainbow trout complementary DNA that encodes a 445 amino acid polypeptide exhibiting an overall 30% homology with human hemopexin and 69% with the goldfish warm temperature acclimation-related 65-kDa protein. Structural homology, deduced from hydrophobic cluster analysis (HCA), was strong between the trout and human proteins since global HCA scores of 76% were obtained when the N- or C-terminal halves of the two proteins were compared. Moreover, several characteristics of hemopexin were found in the trout protein; finally, the trout hemopexin-like messenger RNA was specifically expressed in the liver. We conclude that the trout protein is a good candidate for a true fish hemopexin.