The structural basis of promiscuity in small multidrug resistance transporters

By providing broad resistance to environmental biocides, transporters from the small multidrug resistance (SMR) family drive the spread of multidrug resistance cassettes among bacterial populations. A fundamental understanding of substrate selectivity by SMR transporters is needed to identify the types of selective pressures that contribute to this process. Using solid-supported membrane electrophysiology, we find that promiscuous transport of hydrophobic substituted cations is a general feature of SMR transporters. To understand the molecular basis for promiscuity, we solved X-ray crystal structures of a SMR transporter Gdx-Clo in complex with substrates to a maximum resolution of 2.3 Å. These structures confirm the family’s extremely rare dual topology architecture and reveal a cleft between two helices that provides accommodation in the membrane for the hydrophobic substituents of transported drug-like cations.

Piperine as a Potential Anti-cancer Agent: A Review on Preclinical Studies

Recently many studies showed anticancer activities of piperine, a pungent alkaloid found in black pepper and some other Piper species. We attempted to summarize acquired data that support anticancer potential of this natural agent. Piperine has been reported to possess effective chemopreventive activity. It has been studied to affect via several mechanisms of action, in brief enhancing antioxidant system, increasing level and activity of detoxifying enzymes and suppressing stem cell self-renewal. Moreover, piperine has been found to inhibit proliferation and survival of various cancerous cell lines via modulating cell cycle progression and exhibiting anti-apoptotic activity, respectively. This compound has been shown to modify activity of various enzymes and transcription factors to inhibit invasion, metastasis and angiogenesis. Interestingly, piperine has exhibited antimutagenic activity and also inhibited activity and expression of multidrug resistance transporters such as P-gp and MRP-1. Besides, about all reviewed studies have reported selective cytotoxic activity of piperine on cancerous cells in compared with normal cells. Altogether, the studies completely underline promising candidacy of piperine for further development. The collected preclinical data we provided in this article can be useful in the design of future researches especially clinical trials with piperine.

Substrate polyspecificity and conformational relevance in ABC transporters: new insights from structural studies

Transport of molecules and ions across biological membranes is an essential process in all organisms. It is carried out by a range of evolutionarily conserved primary and secondary transporters. A significant portion of the primary transporters belong to the ATP-binding cassette (ABC) superfamily, which utilise the free-energy from ATP hydrolysis to shuttle many different substrates across various biological membranes, and consequently, are involved in both normal and abnormal physiology. In humans, ABC transporter-associated pathologies are perhaps best exemplified by multidrug-resistance transporters that efflux many xenobiotic compounds due to their remarkable substrate polyspecificity. Accordingly, understanding the transport mechanism(s) is of great significance, and indeed, much progress has been made in recent years, particularly from structural studies on ABC exporters. Consequently, the general mechanism of ‘alternate access’ has been modified to describe individual transporter nuances, though some aspects of the transport process remain unclear. Moreover, as new information has emerged, the physiological relevance of the ‘open-apo’ conformation of MsbA (a bacterial exporter) has been questioned and, by extension, its contribution to mechanistic models. We present here a comprehensive overview of the most recently solved structures of ABC exporters, focusing on new insights regarding the nature of substrate polyspecificity and the physiological relevance of the ‘open-apo’ conformation. This review evaluates the claim that the latter may be an artefact of detergent solubilisation, and we hypothesise that the biophysical properties of the membrane play a key role in the function of ABC exporters allowing them to behave like a ‘spring-hinge’ during their transport cycle.

A Transcriptomics Approach To Unveiling the Mechanisms ofIn VitroEvolution towards Fluconazole Resistance of aCandida glabrataClinical Isolate

ABSTRACTCandida glabratais an emerging fungal pathogen. Its increased prevalence is associated with its ability to rapidly develop antifungal drug resistance, particularly to azoles. In order to unravel new molecular mechanisms behind azole resistance, a transcriptomics analysis of the evolution of aC. glabrataclinical isolate (isolate 044) from azole susceptibility to posaconazole resistance (21st day), clotrimazole resistance (31st day), and fluconazole and voriconazole resistance (45th day), induced by longstanding incubation with fluconazole, was carried out. All the evolved strains were found to accumulate lower concentrations of azole drugs than the parental strain, while the ergosterol concentration remained mostly constant. However, only the population displaying resistance to all azoles was found to have a gain-of-function mutation in theC. glabrataPDR1gene, leading to the upregulation of genes encoding multidrug resistance transporters. Intermediate strains, exhibiting posaconazole/clotrimazole resistance and increased fluconazole/voriconazole MIC levels, were found to display alternative ways to resist azole drugs. Particularly, posaconazole/clotrimazole resistance after 31 days was correlated with increased expression of adhesin genes. This finding led us to identify the Epa3 adhesin as a new determinant of azole resistance. Besides being required for biofilm formation, Epa3 expression was found to decrease the intracellular accumulation of azole antifungal drugs. Altogether, this work provides a glimpse of the transcriptomics evolution of aC. glabratapopulation toward multiazole resistance, highlighting the multifactorial nature of the acquisition of azole resistance and pointing out a new player in azole resistance.