68-3

8/130

(F87V) and IMP-70a4182(pHSG398/IMP-70)1121(pHSG398/IMP-1(F87V))8182(pHSG398/IMP-10)b2142(pHSG398/IMP-1)antibiotic(s)E.coli DH5α (pHSG398）DoripenemImipenemMeropenemPanipenema Iwata S, Tada T, Hishinuma T, et al: Antimicrob Agents Chemother, 2020; 64.18)b IMP-10 and IMP-1(V67F) amino acid arrays are the same≤0.060.125≤0.060.125SubstrateDoripenemImipenemMeropenemPanipenema Iwata S, Tada T, Hishinuma T, et al: Antimicrob Agents Chemother, 2020; 64.18)b Km and kcat were calculated as means ± SD from three independent experiments.MIC(μg/ml)E.coli DH5α kcat/Km (μM-1・s-1)bIMP-10IMP-1(F87V)0.820.240.510.35204Table 4　 Drug susceptibility profiles of E. coli expressing IMP-1, IMP-10, a variant of IMP-1 with an amino acid substitution Table 5　 Kinetic parameters of β-lactamases IMP-1, IMP-10, a variant of IMP-1 with Figure 2　3D structure of IMP-70 MBL and amino acid sequences of IMP-1 and IMP-70 MBLsThese results suggest that, in IMP-70, the Val67Phe amino acid substitution, but not the Phe87Val substitution, is important for the signifi-cantly increased carbapenemase activity against meropenem. The Val67 in IMP-1 is located at the end of “loop1”, close to the active site consisting of amino acids residues 60 to 66 (Figure 2)19). Loop1 is a major determinant for the tight binding of substrates in the active site19). A Val67Phe amino an amino acid substitution (F87V) and IMP-70 with substratesaE.coli DH5α IMP-10.130.230.150.40acid substitution in IMP-43, a variant of IMP-7, has been reported to increase catalytic activities against imipenem and meropenem20). Amino acid substitu-tions at residue 67 in IMP-1 MBLs affect their hydrolytic activity against β-lactams21). Residue 67 was reported to be important for substrate binding in VIM-type MBLs22). Residue 87 plays a crucial role in the stability of VIM-223). IMP-44, a variant of IMP-11 with two substitutions (Val67Phe and E.coli DH5α IMP-700.0910.170.170.240.180.240.350.23E.coli DH5α