{beta}-Lactam Selectivity of Multidrug Transporters AcrB and AcrD Resides in the Proximal Binding Pocket. [Enzymology]

February 20th, 2014 by Kobayashi, N., Tamura, N., van Veen, H. W., Yamaguchi, A., Murakami, S.

β-Lactams are mainstream antibiotics that are indicated for the prophylaxis and treatment of bacterial infections. The AcrA-AcrD-TolC multidrug efflux system confers much stronger resistance on E. coli to clinically relevant anionic β-lactam antibiotics than the homologous AcrA-AcrB-TolC system. Using an extensive combination of chimeric analysis and site-directed mutagenesis, we searched for residues that determine the difference in β-lactam specificity between AcrB and AcrD. We identified three crucial residues at the ″proximal″ (or access) substrate-binding pocket. The simultaneous replacement of these residues in AcrB by those in AcrD (Q569R, I626R and E673G) transferred the β-lactam specificity of AcrD to AcrB. Our findings indicate for the first time that the difference in β-lactam specificity between AcrB and AcrD relates to interactions of the antibiotic with residues in the proximal binding pocket.