Involvement of Aromatic Amino Acids in Phenylmercury Transport by MerT Protein

Abstract

To investigate the role of aromatic amino acids of MerT protein in phenylmercury transport, two merT variants (pMRTm1P and pMRTm2P) with specific site-directed mutations were constructed and examined their effects on C₆H₅Hg⁺-transport. Substitution of Phe-36 and Trp-40 residues located on the periplasmic loop of MerT in turn with Ala and Val, respectively, did not affect the Hg²⁺-uptake, but caused a significant reduction in the C₆H₅Hg⁺-uptake by bacterial cells with intact merT gene. Introduction of specific mutations changing Phe-108, 114, 115 to Ala, and Tyr-110, 116 to Ser in the C-terminal region of the third transmembrane of MerT also caused large reduction in the uptake of C₆H₅Hg⁺, but had no effect on the Hg²⁺-uptake. In addition, both mutations caused a significant reduction in the hypersensitivity to C₆H₅Hg⁺, but without affecting the Hg²⁺-hypersensitive phenotype. Together these results suggest that the aromatic amino acids of MerT protein may play an important role in the transport of C₆H₅Hg⁺ across the cell membrane.