Molecular cloning and characterization of an ATP-binding cassette (ABC) transmembrane transporter from the white shrimp Litopenaeusvannamei.

ATP-binding cassette transmembrane transporters (ABC transporters) have a potential role in drug and xenobiotic resistance. Here, we report for the first time the cloning of an ABC transporter from white shrimp Litopenaeusvannamei (designated LvABCG), along with a study of its phylogenetic relationships, and measurements of its expression in different shrimp tissues exposed to cadmium and pH stress (acidic and alkaline conditions). Sequence analysis showed that LvABCG shares many similarities with the white/ABC transmembrane transporter, including two conserved regions: a highly conserved ATP-binding cassette (ABC) and transmembrane domain (TMD). Spatial analyses of transcript levels for ABCG in shrimp tissues, using reverse transcript PCR, revealed the highest transcript level in the hepatopancreas, less in the intestine and stomach, and none in the other tissues examined. The ABC transporter mRNA transcript in the hepatopancreas of L.vannamei was significantly up-regulated after 1.5 h and 24 h of exposure to alkaline and acidic conditions, respectively. LvABCG was also induced in intestine, but was downregulated in the stomach under the alkaline treatment. Upon exposure to cadmium (4.25 micromol L(-1) and 8.5 micromol L(-1)) for 48 h, the mRNA expression of LvABCG was up-regulated 4.79-fold (at 6 h) and 2.09-fold (at 12 h) in the hepatopancreas. LvABCG was also induced in the stomach after exposure to 4.25 micromol L(-1) cadmium, but downregulated in the stomach and intestine after exposure to 8.5 micromol L(-1) cadmium. These findings indicate that LvABCG might play an important role in the physiological changes related to metabolism and cell detoxification that occur when Pacific white shrimp are exposed to cadmium and pH stress.