RESUMO
The domesticated one-humped camel, Camelus dromedarius, is one of the most important animals in the Arabian Peninsula. For most of its life, this species is exposed to both intrinsic and extrinsic genotoxic factors that cause gross DNA alterations in many organisms. GST enzymes constitute an important supergene family involved in protection against the deleterious effects of oxidative stress and xenobiotics. Cloning the camel mitochondrial GST kappa (GSTK) gene and comparing its structural similarities with different species may aid in understanding its evolutionary relics. We cloned the camel GSTK using RT-PCR. This yielded an open reading frame of 678 nucleotides, encoding a protein of 226 amino acid residues. In a comparative analysis, the cloned GSTK was used to screen orthologues from different organisms. Phylogenetic analysis demonstrated that the camel GSTK apparently evolved from an ancestral GSTK gene that predated the appearance of vertebrates, and it grouped with pig, cattle, dog, horse, human and monkey GSTKs. The calculated molecular weight of the translated ORF was 25.52 kDa and the isoelectric point was 8.4. The deduced cGSTK sequence exhibited high identity with many mammals, such as Bactrian camel (99.55%), pig, cattle and human (>74%), and lower identity with other unrelated organisms, such as frog (Xenopus tropicalis, 61%), chicken (Gallus gallus, 57%), salmon (Salmo salar, 49%), sponge (Amphimedon queenslandica, 46%), tick (Amblyomma maculatum, 45%) and roundworm (Caenorhabditis elegans, 33%). A 3D structure was built based on the crystal structure of the human and rat enzymes. The levels of cGSTK expression in five camel tissues were examined via real-time PCR. The highest level of cGSTK transcripts was found in the camel liver, followed by the testis, spleen, kidney and lung.
