2012年8月12日 讯 /生物谷BIOON/ --刊登在近日的国际杂志Antimicrobial Agents and Chemotherapy上的一篇研究报告中，来自挪威特罗姆瑟大学等处的研究者揭示了绿脓杆菌可移动的金属β内酰胺酶的晶体结构，这就为新型抗生素疗法提供了一些思路。相关研究成果标题为“Crystal Structure of the Mobile Metallo-β-Lactamase AIM-1 from Pseudomonas aeruginosa： Insights into Antibiotic Binding and the Role of Gln157”。
近些年来，由于人们抗生素的滥用，细菌的耐药性不断增强，其中绿脓杆菌就是一种对很多抗生素都具有极强耐药性的菌株，其是院内常见的几大感染性菌株之一，可引发患者肺炎，严重可导致其发展为肺纤维囊肿甚至肺癌。开发治疗绿脓杆菌感染的新型疗法对于临床医生和科学家们都迫在眉睫。
绿脓杆菌的金属β内酰胺酶（MBL）类基因可以介导细菌对β内酰胺类抗生素产生抗性，而且其通过快速可移动的遗传元件来在细菌体内发挥耐药的作用。MBLs包括三个不同的亚族，B1、B2和B3，然而携带可移动MBLs的遗传元件仅仅限于B1亚族。B3 MBLs亚族是一个多分化的亚族，主要负责染色体编码酶类。
绿脓杆菌的AIM-1（Adelaide Imipenmase 1）是第一个发现的B3家族的MBL，在文章中，研究者揭示了AIM-1的晶体结构，并且使用硅对接、量子力学和分子力学的方法进行计算，加上定点诱变的方法来研究AIM-1和β内酰胺类抗生的互作机制。AIM-1采取MBLs典型的αβ/βα三倍折叠股方式，和其它B3酶类不一样，其它B3酶类使用二硫键形成的方式。研究结果表明，AIM-1的底物结合部位相比其它B3 MBLs非常狭窄而且严格，这也解释了其高度的催化活性。
研究者发现，紧邻AIM-1的Gln157锌中心或许可以成为药物的结合靶点，然而AIM-1残基Asn和Ala的移去会影响到其活性，这也就揭示了这两个残基的重要性。最后研究者Samuelsen表示，我们的研究揭示了AIM-1是B3 MBL的一个亚类，其具有新型的晶体结构和机械特性。（生物谷Bioon.com）
doi:10.1128/AAC.00448-12
PMC:
PMID:
Crystal Structure of the Mobile Metallo-β-Lactamase AIM-1 from Pseudomonas aeruginosa: Insights into Antibiotic Binding and the Role of Gln157
Hanna-Kirsti S. Leirosa, Pardha S. Borrab, Bjørn Olav Brandsdala,c, Kine Susann Waade Edvardsena, James Spencerd, Timothy R. Walshe and Ørjan Samuelsenf
Metallo-β-lactamase (MBL) genes confer resistance to virtually all β-lactam antibiotics and are rapidly disseminated by mobile genetic elements in Gram-negative bacteria. MBLs belong to three different subgroups, B1, B2, and B3, with the mobile MBLs largely confined to subgroup B1. The B3 MBLs are a divergent subgroup of predominantly chromosomally encoded enzymes. AIM-1 (Adelaide IMipenmase 1) from Pseudomonas aeruginosa was the first B3 MBL to be identified on a readily mobile genetic element. Here we present the crystal structure of AIM-1 and use in silico docking and quantum mechanics and molecular mechanics (QM/MM) calculations, together with site-directed mutagenesis, to investigate its interaction with β-lactams. AIM-1 adopts the characteristic αβ/βα sandwich fold of MBLs but differs from other B3 enzymes in the conformation of an active site loop (residues 156 to 162) which is involved both in disulfide bond formation and, we suggest, interaction with substrates. The structure, together with docking and QM/MM calculations, indicates that the AIM-1 substrate binding site is narrower and more restricted than those of other B3 MBLs, possibly explaining its higher catalytic efficiency. The location of Gln157 adjacent to the AIM-1 zinc center suggests a role in drug binding that is supported by our in silico studies. However, replacement of this residue by either Asn or Ala resulted in only modest reductions in AIM-1 activity against the majority of β-lactam substrates, indicating that this function is nonessential. Our study reveals AIM-1 to be a subclass B3 MBL with novel structural and mechanistic features.
