Effects of engineering complementary charged residues into the hydrophobic subunit interface of tyrosyl-tRNA synthetase

Wild-type tyrosyl-tRNA synthetase (TyrTS) from Bacillus stearothermophilus is a symmetrical dimer. Four different heterodimeric enzymes have been produced by site-directed mutagenesis at the subunit interface so that the monomers are linked by a potential salt bridge in a hydrophobic environment. The two Phe-164 residues of wild-type TyrTS are on the axis of symmetry and interact in hydrophobic region of the subunit interface. Mutation of Phe-164 to aspartate or glutamate in full-length TyrTS and to lysine or arginine in an active truncated enzyme ( Delta TyrTS) induces reversible dissociation of the enzyme into inactive monomers.