Adler Julia, Lewinson Oded, Bibi Eitan
Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
Biochemistry. 2004 Jan 20;43(2):518-25. doi: 10.1021/bi035485t.
According to the current topology model of the Escherichia coli multidrug transporter MdfA, it contains a membrane-embedded negatively charged residue, Glu26, which was shown to play an important role in substrate recognition. To further elucidate the role of this substrate recognition determinant, various Glu26 replacements were characterized. Surprisingly, studies with neutral MdfA substrates showed that, unlike many enzymatic systems where the size and chemical properties of binding site residues are relatively defined, MdfA tolerates a variety of changes at position 26, including size, hydrophobicity, and charge. Moreover, although efficient transport of positively charged substrates requires a negative charge at position 26 (Glu or Asp), neutralization of this charge does not always abrogate the interaction of MdfA with cationic drugs, thus demonstrating that the negative charge does not play an essential role in the multidrug transport mechanism. Collectively, these results suggest a link between the broad substrate specificity profile of multidrug transporters and the structural and chemical promiscuity at their substrate recognition pockets.
根据目前大肠杆菌多药转运蛋白MdfA的拓扑模型，它含有一个嵌入膜内的带负电荷残基Glu26，已证明该残基在底物识别中起重要作用。为了进一步阐明这个底物识别决定因素的作用，对各种Glu26替代物进行了表征。令人惊讶的是，对中性MdfA底物的研究表明，与许多酶系统中结合位点残基的大小和化学性质相对确定不同，MdfA在第26位耐受多种变化，包括大小、疏水性和电荷。此外，虽然带正电荷底物的有效转运需要第26位带负电荷（Glu或Asp），但该电荷的中和并不总是消除MdfA与阳离子药物的相互作用，因此表明负电荷在多药转运机制中并不起关键作用。总体而言，这些结果表明多药转运蛋白广泛的底物特异性谱与其底物识别口袋处的结构和化学混杂性之间存在联系。
