A New Twist in ABC Transporter Mediated Multidrug Resistance - Pdr5 is a Drug/proton Co-transporter.

The two major efflux pump systems that are involved in multidrug resistance (MDR) are (i) ATP binding cassette (ABC) transporters and (ii) secondary transporters. While the former use binding and hydrolysis of ATP to facilitate export of cytotoxic compounds, the latter utilize electrochemical gradients to expel their substrates. Pdr5 from Saccharomyces cerevisiae is a prominent member of eukaryotic ATP binding cassette (ABC) transporters that are involved in multidrug resistance (MDR) and used as a frequently studied model system. Although investigated for decades, the underlying molecular mechanisms of drug transport and substrate specificity remain elusive. Here, we provide electrophysiological data on the reconstituted Pdr5 demonstrating that this MDR efflux pump does not only actively translocate its substrates across the lipid bilayer, but at the same time generates a proton motif force in the presence of Mg2+-ATP and substrates by acting as a proton/drug co-transporter. Importantly, a strictly substrate dependent co-transport of protons was also observed in in vitro transport studies using Pdr5-enriched plasma membranes. We conclude from these results that the mechanism of MDR conferred by Pdr5 and likely other transporters is more complex than the sole extrusion of cytotoxic compounds and involves secondary coupled processes suitable to increase the effectiveness.

Flipping and other astonishing transporter dance moves in fungal drug resistance.

In all domains of life, transmembrane proteins from the ATP-binding cassette (ABC) transporter family drive the translocation of diverse substances across lipid bilayers. In pathogenic fungi, the ABC transporters of the pleiotropic drug resistance (PDR) subfamily confer antibiotic resistance and so are of interest as therapeutic targets. They also drive the quest for understanding how ABC transporters can generally accommodate such a wide range of substrates. The Pdr5 transporter from baker's yeast is representative of the PDR group and, ever since its discovery more than 30 years ago, has been the subject of extensive functional analyses. A new perspective of these studies has been recently provided in the framework of the first electron cryo-microscopy structures of Pdr5, as well as emergent applications of machine learning in the field. Taken together, the old and the new developments have been used to propose a mechanism for the transport process in PDR proteins. This mechanism involves a "flippase" step that moves the substrates from one leaflet of the bilayer to the other, as a central element of cellular efflux.

Structure and efflux mechanism of the yeast pleiotropic drug resistance transporter Pdr5.

Pdr5, a member of the extensive ABC transporter superfamily, is representative of a clinically relevant subgroup involved in pleiotropic drug resistance. Pdr5 and its homologues drive drug efflux through uncoupled hydrolysis of nucleotides, enabling organisms such as baker's yeast and pathogenic fungi to survive in the presence of chemically diverse antifungal agents. Here, we present the molecular structure of Pdr5 solved with single particle cryo-EM, revealing details of an ATP-driven conformational cycle, which mechanically drives drug translocation through an amphipathic channel, and a clamping switch within a conserved linker loop that acts as a nucleotide sensor. One half of the transporter remains nearly invariant throughout the cycle, while its partner undergoes changes that are transmitted across inter-domain interfaces to support a peristaltic motion of the pumped molecule. The efflux model proposed here rationalises the pleiotropic impact of Pdr5 and opens new avenues for the development of effective antifungal compounds.

Health economic evaluation of an infection prevention and control program: are quality and patient safety programs worth the investment?

BACKGROUND: The effect of regional consolidation of an infection prevention and control (IPC) program on reduction of selected health care-acquired infections (HAIs), the economic burden of these illnesses, and where the potential for greatest financial benefit in reducing infection rates lies was assessed. METHODS: Cost-benefit analysis (in Canadian $) was used to evaluate the effectiveness of a regional IPC program in preventing incident cases of HAIs. The costs of managing these infections, as well as the operational costs of the IPC program were compared against reductions in HAI rates over a 4-year period. Benefits were calculated as cost avoided by reducing HAI cases year over year. RESULTS: The Health Authority spent more than $66.3 million managing 24,937 HAI cases over the 4-year evaluation period. Urinary tract infections, methicillin-resistant Staphylococcus aureus, and bacteremias incurred the greatest costs. A reduction of 4,739 HAI cases led to avoided costs of $9.1 million in 4 years; the IPC program budget was $6.7 million during this period. CONCLUSION: Regionalization of the IPC program with standardized policies, procedures, and initiatives led to a 19% reduction in selected HAIs over 4 years and a cost avoidance of at least $9 million. This was particularly evident in years 3 and 4 of the program when $7.2 million (79% of the total) savings were realized.