Implication of Ile-69 and Thr-182 residues in kinetic characteristics of IRT-3 (TEM-32) beta-lactamase

The substitution of a methionine for an isoleucine at position 69 (Met69Ile), which causes inhibitor resistance to TEM-type beta-lactamases (IRT-3 and IRT-I69), altered the positions of the Asn-170 and Glu-166 side chains as well as the position of the catalytic water molecule. A novel hydrogen bond between the hydroxyl of Thr-182 and the carbonyl of Glu-64 was expected to be responsible for the increase in the catalytic activity of the IST-T182 and IRT-3 enzymes compared with those of TEM-1 and IRT-169, respectively.