Three nucleus-encoded subunits of mitochondrial cytochrome c oxidase of the whiteleg shrimp Litopenaeus vannamei: cDNA characterization, phylogeny and mRNA expression during hypoxia and reoxygenation

The mitochondrial cytochrome c oxidase (COX) catalyzes the reduction of oxygen to water playing a key role in the respiratory chain and ATP synthesis. The nucleus-encoded COX subunits do not participate in catalysis, but some are known to play a role in the expression, assembly and activity of the enzyme. Since hypoxia continuously affects the shrimp environment, it is important to study COX to understand their ability to deal with low oxygen levels. The goal of this research was to characterize the complementary DNA (cDNA) sequences of three nucleus-encoded subunits —coxIV, coxVa, and coxVb— and to evaluate the shrimp COX response to hypoxia by measuring their gene expression. The cDNA sequence of coxIV consisted of 532 bp, which encodes a 17.47 kDa protein, while coxVa cDNA consisted of 460 bp and coded a protein of 17.11 kDa, and the coxVb coding sequence consisted of 364 bp encoding a 13.74 kDa protein. Shrimp subunits do not have isoforms, and they are not differentially expressed during hypoxia, as observed in mammals. Coordinated changes were detected in the mRNA amounts of nuclear and mitochondrial subnits; these changes, at the transcriptional level, are suggested to be controlled through transcriptional factors Sp1 and NRF2.