The new AqE gene studied in non-tetrapoda vertebrates is high conserved

Abstract

Background: The AqE gene encoding the NAD(P)H-dependent LDH2/MDH2 oxidoreductase has been described in living organisms predominantly in the aquatic environment. It was shown that the gene is present in bacteria and archaea. In the plant kingdom this gene is present only in algae. Animals have the AqE gene in all groups, from protozoa to fish. In the ancestor of tetrapods, the gene disappears and, accordingly, is absent in amphibians, reptiles, birds and mammals. It was suggested that the gene is involved in anaerobic respiration. The loss of the AqE gene in animals and plants is likely to be associated with living on land and the corresponding restructuring of their metabolic pathways, due to oxygen saturation and the absence of natural hypoxia as in aquatic organisms Results: A study of the distribution of the AqE gene among non-tetrapoda vertebrates showed that it is present in the genomes of bony and cartilaginous fishes, as well as in the genomes of hagfishes and lampreys. In addition, it was reliably shown that, for representatives of Cypriniformes, the AqE gene was lost, and for representatives of Salmoniformes, it underwent significant deletions, which most likely led to its pseudogenization. Conclusions: In most orders of non-tetrapoda vertebrates, the AqE gene remains highly conserved. This suggests that the AqE in aquatic vertebrates is an essential gene and undergoes to rigorous selection. AqE gene has the highest homology with the archaeal ComC that encoding SLDH. Based on the similarity of substrates, it cannot be excluded that the enzyme encoded by the AqE gene is involved in the malate-aspartate shuttle mechanism or biosynthesis of energy coenzyme M equivalent.