Uncovering the functioning of a multidrug efflux pump of Streptococcus pneumoniae involved in fluoroquinolone ResIStancE – Multidrug-RISE

Multidrug efflux pumps are major players in antibiotic resistance. Despite a better understanding of their global functioning mechanism, how they work in vivo (with respect to the bio-availability and partition of the drugs in the bacteria) and what is their intimate molecular mechanism (spectrum of drug recognition, nucleotide hydrolysis mechanism ?) remain obscure. We will focus on a multidrug ABC (“ATP-Binding Cassette”) transporter involved in resistance to fluoroquinolones (FQ) in clinical setting. This transporter functions according to an asymmetric catalytic cycle, its two nucleotide-binding sites being functionally non-equivalent. It also shows a strong preference for GTP as the energy source, unlike most ABC proteins, thereby defining a new sub-family of ABC transporters. We will address burning questions regarding (i) the molecular determinants that dictate its preference for GTP; (ii) the intimate catalytic mechanism of GTPase and ATPase activities and the respective role of its two nucleotide-binding sites in these processes; (iii) the presumed interaction with nucleoside diphosphate kinase and how this strengthens its preference for GTP; (iv) the poly-specificity of recognition and efflux of the FQ, by combining the molecular bases at the transporter level with the bio-availability of FQ inside the bacteria. Our results will allow a fine understanding of the contribution and molecular functioning of a multidrug transporter involved in the clinical resistance to FQ.