Ross J I, Eady E A, Cove J H, Cunliffe W J, Baumberg S, Wootton J C
Department of Microbiology, University of Leeds, UK.
Mol Microbiol. 1990 Jul;4(7):1207-14. doi: 10.1111/j.1365-2958.1990.tb00696.x.
A Staphylococcus epidermidis plasmid conferring inducible resistance to 14-membered ring macrolides and type B streptogramins has been analysed and the DNA sequence of the gene responsible for resistance determined. A single open reading frame of 1.464 kbp, preceded by a complex control region containing a promoter and two ribosomal binding sites, was identified. The deduced sequence of the 488-amino-acid protein (MsrA) revealed the presence of two ATP-binding motifs homologous to those of a family of transport-related proteins from Gram-negative bacteria and eukaryotic cells, including the P-glycoprotein responsible for multidrug resistance. In MsrA, but not these other proteins, the two potential ATP-binding domains are separated by a Q-linker of exceptional length. Q-linkers comprise a class of flexible interdomain fusion junctions that are typically rich in glutamine and other hydrophilic amino acids and have a characteristic spacing of hydrophobic amino acids, as found in the MsrA sequence. Unlike the other transport-related proteins, which act in concert with one or more hydrophobic membrane proteins, MsrA appears to function independently when cloned in a heterologous host (Staphylococcus aureus RN4220). MsrA might, therefore, interact with and confer antibiotic specificity upon other transmembrane efflux complexes of staphylococcal cells. The active efflux of [14C]-erythromycin from cells of S. aureus RN4220 containing msrA has been demonstrated.
已对一种赋予对14元环大环内酯类和B型链阳菌素诱导抗性的表皮葡萄球菌质粒进行了分析，并确定了负责抗性的基因的DNA序列。鉴定出一个1.464 kbp的单一开放阅读框，其前面是一个包含启动子和两个核糖体结合位点的复杂控制区域。推导的488个氨基酸的蛋白质（MsrA）序列显示存在两个与革兰氏阴性细菌和真核细胞中一类与转运相关的蛋白质的ATP结合基序同源，包括负责多药耐药性的P-糖蛋白。在MsrA中，但在其他这些蛋白质中没有，两个潜在的ATP结合结构域被一个异常长的Q连接子隔开。Q连接子包括一类灵活的结构域间融合连接，通常富含谷氨酰胺和其他亲水氨基酸，并且具有如MsrA序列中发现的疏水氨基酸的特征间距。与其他与转运相关的蛋白质不同，后者与一种或多种疏水膜蛋白协同作用，MsrA在克隆到异源宿主（金黄色葡萄球菌RN4220）中时似乎独立发挥作用。因此，MsrA可能与葡萄球菌细胞的其他跨膜外排复合物相互作用并赋予抗生素特异性。已经证明含有msrA的金黄色葡萄球菌RN4220细胞中[14C] - 红霉素的活性外排。
