It is now well-known that the enhanced expression of ATP binding cassette (ABC) and major facilitator superfamily (MFS) proteins contribute to the development of tolerance to antifungals in yeasts. For example, the azole resistant clinical isolates of the opportunistic human fungal pathogen Candida albicans show an overexpression of Cdr1p and/or CaMdr1p belonging to ABC and MFS superfamilies, respectively. Hence, azole resistant isolates display reduced accumulation of therapeutic drug due to its rapid extrusion and that facilitates its survival. Considering the importance of major antifungal transporters, the focus of recent research has been to understand the structure and function of these proteins to design inhibitors/modulators to block the pump protein activity so that the drug already in use could again sensitize resistant yeast cells. The review focuses on the structure and function of ABC and MFS transporters of Candida to highlight the recent advancement in the field.

In the present study, we have investigated the antifungal effects of a natural polyphenol, CUR (curcumin), against albicans and non-albicans species of Candida and have shown its ability to inhibit the growth of all the tested strains. The inhibitory effects of CUR were independent of the status of the multidrug efflux pump proteins belonging to either ABC transporter (ATP-binding cassette transporter) or MFS (major facilitator) superfamilies of transporters. By using a systemic murine model of infection, we established that CUR and piperine, when administered together, caused a significant fungal load reduction (1.4log₁₀) in kidneys of Swiss mice. Additionally, CUR raised the levels of ROS (reactive oxygen species), which, as revealed by annexin V–FITC labelling, triggered early apoptosis in Candida cells. Coincident with the raised ROS levels, mRNAs of tested oxidative stress-related genes [CAP1 (Candida albicans AP-1), CaIPF7817 (putative NADH-dependent flavin oxidoreductase), SOD2 (superoxide dismutase 2), GRP2 (NADPH-dependent methyl glyoxal reductase) and CAT1 (catalase 1)] were also elevated. The growth inhibitory effects of CUR could be reversed by the addition of natural and synthetic antioxidants. Notably, independent of ROS status, polyphenol CUR prevented hyphae development in both liquid and solid hypha-inducing media by targeting the global suppressor TUP1 (thymidine uptake 1). Taken together, our results provide the first evidence that CUR acts as an antifungal agent, via generation of oxidative stress, and inhibits hyphae development by targeting TUP1.

The global pandemic crisis, coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has claimed the lives of millions of people across the world. Development and testing of anti-SARS-CoV-2 drugs or vaccines have not turned to be realistic within the timeframe needed to combat this pandemic. Here, we report a comprehensive computational approach to identify the multi-targeted drug molecules against the SARS-CoV-2 proteins, whichare crucially involved in the viral–host interaction, replication of the virus inside the host, disease progression and transmission of coronavirus infection. Virtual screening of 75 FDA-approved potential antiviral drugs against the target proteins, spike (S) glycoprotein, human angiotensin-converting enzyme 2 (hACE2), 3-chymotrypsin-like cysteine protease (3CLpro), cathepsin L (CTSL), nucleocapsid protein, RNA-dependent RNA polymerase (RdRp) and non-structural protein 6 (NSP6), resulted in the selection of seven drugs which preferentially bind to the target proteins. Further, the molecular interactions determined by molecular dynamics simulation revealed that among the 75 drug molecules, catechin can effectively bind to 3CLpro, CTSL, RBD of S protein, NSP6 and nucleocapsid protein. It is more conveniently involved in key molecular interactions, showing binding free energy (ΔGbind) in the range of −5.09 kcal/mol (CTSL) to −26.09 kcal/mol (NSP6). At the binding pocket, catechin is majorly stabilized by the hydrophobic interactions, displays ΔEvdW values: −7.59 to −37.39 kcal/mol. Thus, the structural insights of better binding affinity and favorable molecular interaction of catechin toward multiple target proteins signify that catechin can be potentially explored as a multi-targeted agent against COVID-19.

Candida albicans causes superficial to systemic infections in immuno-compromised individuals. The concomitant use of fungistatic drugs and the lack of cidal drugs frequently result in strains that could withstand commonly used antifungals, and display multidrug resistance (MDR). In search of novel fungicidals, in this study, we have explored a plant alkaloid berberine (BER) for its antifungal potential. For this, we screened an in-house transcription factor (TF) mutant library of C. albicans strains towards their susceptibility to BER. Our screen of TF mutant strains identified a heat shock factor (HSF1), which has a central role in thermal adaptation, to be most responsive to BER treatment. Interestingly, HSF1 mutant was not only highly susceptible to BER but also displayed collateral susceptibility towards drugs targeting cell wall (CW) and ergosterol biosynthesis. Notably, BER treatment alone could affect the CW integrity as was evident from the growth retardation of MAP kinase and calcineurin pathway null mutant strains and transmission electron microscopy. However, unlike BER, HSF1 effect on CW appeared to be independent of MAP kinase and Calcineurin pathway genes. Additionally, unlike hsf1 null strain, BER treatment of Candida cells resulted in dysfunctional mitochondria, which was evident from its slow growth in non-fermentative carbon source and poor labeling with mitochondrial membrane potential sensitive probe. This phenotype was reinforced with an enhanced ROS levels coinciding with the up-regulated oxidative stress genes in BER-treated cells. Together, our study not only describes the molecular mechanism of BER fungicidal activity but also unravels a new role of evolutionary conserved HSF1, in MDR of Candida.

ABC (ATP binding cassette) and MFS (major facilitator superfamily) exporters, belonging to two different super-families, are one of the most prominent contributors of multidrug resistance (MDR) in yeast. While the role of ABC efflux pump proteins in the development of MDR is well documented, the MFS transporters which are also implicated in clinical drug resistance have not received due attention. The MFS superfamily is the largest known family of secondary active membrane carriers, and MFS exporters are capable of transporting a host of substrates ranging from small molecules, including organic and inorganic ions, to complex biomolecules, such as peptide and lipid moieties. A few of the members of the drug/H⁺ antiporter (DHA) sub-family of the MFS superfamily function as multidrug transporters and employ downhill transport of protons to efflux their respective substrates. This review focuses on the recent developments in MFS of Candida and highlights their role in drug transport by using the example of the relatively well characterized promiscuous Mdr1 efflux pump of the pathogenic yeast Candida albicans.