Conformational changes in a bacterial multidrug transporter are phosphatidylethanolamine-dependent
Conformational changes in a bacterial multidrug transporter are phosphatidylethanolamine-dependent
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DOI：
10.1007/s00018-007-7031-0
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发表时间：
2007-06-01
影响因子：
8
通讯作者：
Ruysschaert, J.-M.
中科院分区：
文献类型：
--
作者：
Gbaguidi, B.;Hakizimana, P.;Ruysschaert, J.-M.
LmrP是一种产电H+/药物反向转运蛋白，可挤出广谱抗生素。五个羧基残基涉及药物结合（Asp 142和Glu 327）和质子动力介导的重组（Asp 68，Asp 128和Asp 235）。ATR-FTIR（衰减全反射-傅里叶变换红外）和色氨酸淬灭实验表明，需要磷脂酰乙醇胺（PE）产生的结构中间体诱导电离的羧基残基。令人惊讶的是，没有电离诱导的构象变化是可检测到的PE的情况下，这表明羧酸残基不取代或电离不会导致任何构象变化。对于在PE脂质体中复溶的LmrP，通过ATR-FTIR光谱法评价的羧酸残基的平均pKa为6.5，而在不存在PE的情况下计算的pKa为4.6。考虑到19个羧基残基中的16个位于膜外环中，在不存在和存在PE的情况下获得的pKa值表明，环酸残基与膜界面的相互作用取决于脂质组合物。
LmrP is an electrogenic H+/drug antiporter that extrudes a broad spectrum of antibiotics. Five carboxylic residues are implicated in drug binding (Asp142 and Glu327) and proton motive force-mediated restructuring (Asp68, Asp128 and Asp235). ATR-FTIR (Attenuated Total Reflection - Fourier Transform Infrared) and tryptophan quenching experiments revealed that phosphatidylethanolamine (PE) is required to generate the structural intermediates induced by ionization of carboxylic residues. Surprisingly, no ionization-induced conformational changes were detectable in the absence of PE, suggesting either that carboxylic acid residues do not ionize or that ionization does not lead to any conformational change. The mean pKa of carboxylic residues evaluated by ATR-FTIR spectroscopy was 6.5 for LmrP reconstituted in PE liposomes, whereas the pKa calculated in the absence of PE was 4.6. Considering that 16 of the 19 carboxylic residues are located in the extramembrane loops, the pKa values obtained in the absence and in the presence of PE suggest that the interaction of the loop acid residues with the membrane interface depends on the lipid composition.