Site-directed mutagenesis studies of selected motif and charged residues and of cysteines of the multifunctional tetracycline efflux protein Tet(L)

All of the transmembrane glutamates of Tet(L) are essential for tetracycline (TET) resistance, and E397 has been shown to be essential for all catalytic modes, i.e., TET-Me²⁺ and Na⁺ efflux and K⁺ uptake. Loop residues D74 and G70 are essential for TET flux but not for Na⁺ or K⁺ flux. A cysteineless Tet(L) protein exhibits all activities.