An Undecaprenyl Phosphate-Aminoarabinose Flippase Required for Polymyxin Resistance in Escherichia coli*
An Undecaprenyl Phosphate-Aminoarabinose Flippase Required for Polymyxin Resistance in Escherichia coli*
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DOI：
10.1074/jbc.m706172200
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发表时间：
2007-12
影响因子：
4.8
通讯作者：
Aixin Yan;Z. Guan;C. Raetz
中科院分区：
文献类型：
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作者：
Aixin Yan;Z. Guan;C. Raetz
用4-氨基-4-脱氧-1-阿拉伯糖（I-Ara 4 N）部分修饰脂质A是大肠杆菌和鼠伤寒沙门氏菌中对多粘菌素和阳离子抗微生物肽的抗性所必需的。一个由七个基因组成的操纵子（在S. typhimurium），其受PmrA转录因子调节，并且也存在于E.大肠杆菌中，是维持多粘菌素抗性所必需的。我们先前阐明了pmrHFIJK在l-Ara 4 N的生物合成和与脂质A的连接中的作用，并分别将这些基因重命名为arn-BCADT。我们现在提出操纵子的最后两个基因pmrL和pmrM的功能。染色体失活的每一个这些基因在一个E。coli pmrAc亲本的表型由多粘菌素抗性转变为多粘菌素敏感。脂质A不再被I-Ara 4 N修饰，即使I-Ara 4 N部分的脂质连接的供体一一磷酸十一异戊烯酯-α-I-Ara 4 N的水平在突变体中没有降低。然而，存在于突变体中的十一异戊二烯基磷酸-α-l-Ara 4 N在内膜的周质表面上的浓度较低，如通过用内膜不可渗透的胺试剂N-羟基磺基琥珀酰亚胺-亚氨基生物素标记的4-5倍减少所判断的。在相同pmrAc亲本的arnT突变体中，其缺乏将I-Ara 4 N单元转移至脂质A的酶，但保留与亲本相同的高水平的十一异戊二烯基磷酸-α-I-Ara 4 N，N-羟基磺基琥珀酰亚胺生物素标记没有减少。这些结果表明pmrL和pmrM，而不是arnT，在运输十一异戊二烯磷酸-α-l-Ara 4 N穿过内膜。PmrM和PmrL，由于它们参与脂质A的l-Ara 4 N修饰，现在更名为阿恩和ArnF，可能是十一异戊二烯磷酸-α-l-Ara 4 N翻转酶的亚基。
Modification of lipid A with the 4-amino-4-deoxy-l-arabinose (l-Ara4N) moiety is required for resistance to polymyxin and cationic antimicrobial peptides in Escherichia coli and Salmonella typhimurium. An operon of seven genes (designated pmrHFIJKLM in S. typhimurium), which is regulated by the PmrA transcription factor and is also present in E. coli, is necessary for the maintenance of polymyxin resistance. We previously elucidated the roles of pmrHFIJK in the biosynthesis and attachment of l-Ara4N to lipid A and renamed these genes arn-BCADT, respectively. We now propose functions for the last two genes of the operon, pmrL and pmrM. Chromosomal inactivation of each of these genes in an E. coli pmrAc parent switched its phenotype from polymyxin-resistant to polymyxin-sensitive. Lipid A was no longer modified with l-Ara4N, even though the levels of the lipid-linked donor of the l-Ara4N moiety, undecaprenyl phosphate-α-l-Ara4N, were not reduced in the mutants. However, the undecaprenyl phosphate-α-l-Ara4N present in the mutants was less concentrated on the periplasmic surface of the inner membrane, as judged by 4-5-fold reduced labeling with the inner membrane-impermeable amine reagent N-hydroxysulfosuccin-imidobiotin. In an arnT mutant of the same pmrAc parent, which lacks the enzyme that transfers the l-Ara4N unit to lipid A but retains the same high levels of undecaprenyl phosphate-α-l-Ara4N as the parent, N-hydroxysulfosuccinimidobiotin labeling was not reduced. These results implicate pmrL and pmrM, but not arnT, in transporting undecaprenyl phosphate-α-l-Ara4N across the inner membrane. PmrM and PmrL, now renamed ArnE and ArnF because of their involvement in l-Ara4N modification of lipid A, may be subunits of an undecaprenyl phosphate-α-l-Ara4N flippase.