Decreased function of the class B tetracycline efflux protein Tet with mutations at aspartate 15, a putative intramembrane residue

The role of the aspartate 15 residue of the class B tetracycline efflux protein Tet was studied, using site-directed mutagenesis in Escherichia coli. Replacement of aspartate by tyrosine, histidine or asparagine resulted in a reduction in tetracycline resistance. The tyrosine and histidine substitutions lowered the Vmax of tetracycline transport but did not change the Km. On the other hand, the asparagine substitution increased the Km but did not change the Vmax. Therefore, Asp-15 could play a role in Tet efflux.