Department of Chemistry, Nara Medical University, 840 Shojo-Cho, Kashihara, Nara 634-8521, Japan.
Institute for Protein Research, Osaka University, 3-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
J Biochem. 2022 Dec 27;173(1):21-30. doi: 10.1093/jb/mvac080.
IMP-type metallo-β-lactamases confer resistance to carbapenems and a broad spectrum of β-lactam antibiotics. IMP-6 and IMP-1 differ by only a point mutation: Ser262 in IMP-1 and Gly262 in IMP-6. The kcat/Km values of IMP-1 for imipenem and meropenem are nearly identical; however, for IMP-6, the kcat/Km for meropenem is 7-fold that for imipenem. In clinical practice, this may result in an ineffective therapeutic regimen and, consequently, in treatment failure. Here, we report the crystal structures of IMP-6 and IMP-1 with the same space group and similar cell constants at resolutions of 1.70 and 1.94 Å, respectively. The overall structures of IMP-6 and IMP-1 are similar. However, the loop region (residues 60-66), which participates in substrate binding, is more flexible in IMP-6 than in IMP-1. This difference in flexibility determines the substrate specificity of IMP-type metallo-β-lactamases for imipenem and meropenem. The amino acid at position 262 alters the mobility of His263; this affects the flexibility of the loop via a hydrogen bond with Pro68, which plays the role of a hinge in IMP-type metallo-β-lactamases. The substitution of Pro68 with a glycine elicited an increase in the Km of IMP-6 for imipenem, whereas the affinity for meropenem remained unchanged.
IMP 型金属β-内酰胺酶对碳青霉烯类和广谱β-内酰胺类抗生素具有耐药性。IMP-6 和 IMP-1 仅相差一个点突变：IMP-1 中的丝氨酸 262 和 IMP-6 中的甘氨酸 262。IMP-1 对亚胺培南和美罗培南的 kcat/Km 值几乎相同；然而，对于 IMP-6，美罗培南的 kcat/Km 是亚胺培南的 7 倍。在临床实践中，这可能导致治疗方案无效，从而导致治疗失败。在这里，我们报道了 IMP-6 和 IMP-1 的晶体结构，它们具有相同的空间群和相似的晶胞常数，分辨率分别为 1.70 和 1.94 Å。IMP-6 和 IMP-1 的整体结构相似。然而，参与底物结合的环区（残基 60-66）在 IMP-6 中比在 IMP-1 中更具柔性。这种柔性差异决定了 IMP 型金属β-内酰胺酶对亚胺培南和美罗培南的底物特异性。位置 262 的氨基酸改变了 His263 的迁移率；这通过与 Pro68 的氢键影响环的柔性，Pro68 在 IMP 型金属β-内酰胺酶中起铰链作用。用甘氨酸取代 Pro68 会导致 IMP-6 对亚胺培南的 Km 增加，而对美罗培南的亲和力保持不变。
