Mitochondrial uncoupling proteins UCP4 and UCP5 from the Pacific white shrimp Litopenaeus vannamei

Mitochondrial uncoupling proteins (UCP) transport protons from the intermembrane space to the mitochondrial matrix uncoupling oxidative phosphorylation. In mammals, these proteins have been implicated in several cellular functions ranging from thermoregulation to antioxidant defense. In contrast, their invertebrate homologs have been much less studied despite the great diversity of species. In this study, two transcripts encoding mitochondrial uncoupling proteins were, for the first time, characterized in crustaceans. The white shrimp Litopenaeus vannamei transcript LvUCP4 is expressed in all tested shrimp tissues/organs, and its cDNA includes a coding region of 954bp long which encodes a deduced protein 318 residues long and a predicted molecular weight of 35.3kDa. The coding region of LvUCP5 transcript is 906bp long, encodes a protein of 302 residues with a calculated molecular weight of 33.17kDa. Both proteins share homology with insect UCPs, their predicted structures show the conserved motifs of the mitochondrial carrier proteins and were confirmed to be located in the mitochondria through a Western blot analysis. The genic expression of LvUCP4 and LvUCP5 was evaluated in shrimp at oxidative stress conditions and results were compared to some antioxidant enzymes to infer about their antioxidant role. LvUCP4 and LvUCP5 genes expression did not change during hypoxia/re-oxygenation, and no coordinated responses were detected with antioxidant enzymes at the transcriptional level. Results confirmed UCPs as the first uncoupling mechanism reported in this species, but their role in the oxidative stress response remains to be confirmed.