Advances in targeting the vacuolar proton-translocating ATPase (V-ATPase) for anti-fungal therapy

Abstract

Vacuolar proton-translocating ATPase (V-ATPase) is a membrane-bound, multi-subunit enzyme that uses the energy of ATP hydrolysis to pump protons across membranes. V-ATPase activity is critical for pH homeostasis and organelle acidification as well as for generation of the membrane potential that drives secondary transporters and cellular metabolism. V-ATPase is highly conserved across species and is best characterized in the model fungus Saccharomyces cerevisiae. However, recent studies in mammals have identified significant alterations from fungi, particularly in the isoform composition of the 14 subunits and in the regulation of complex disassembly. These differences could be exploited for selectivity between fungi and humans and highlight the potential for V-ATPase as an anti-fungal drug target. Candida albicans is a major human fungal pathogen and causes fatality in 35% of systemic infections, even with anti-fungal treatment. The pathogenicity of C. albicans correlates with environmental, vacuolar, and cytoplasmic pH regulation, and V-ATPase appears to play a fundamental role in each of these processes. Genetic loss of V-ATPase in pathogenic fungi leads to defective virulence, and a comprehensive picture of the mechanisms involved is emerging. Recent studies have explored the practical utility of V-ATPase as an anti-fungal drug target in C. albicans, including pharmacological inhibition, azole therapy, and targeting of downstream pathways. This overview will discuss these studies as well as hypothetical ways to target V-ATPase and novel high-throughput methods for use in future drug discovery screens.

The Contribution of Candida albicans Vacuolar ATPase Subunit V 1 B, Encoded by VMA2 , to Stress Response, Autophagy, and Virulence Is Independent of Environmental pH

“…V-ATPase mutants are also impaired in vacuolar biogenesis due to defects in both vacuolar membrane fusion and fission (7). In addition to its requirement for intraorganellar pH homeostasis, V-ATPase function has been implicated in cytosolic and extracellular pH homeostasis (1,(8)(9)(10)(11), underscoring the far-reaching importance of this pump to overall cellular homeostasis. V-ATPase inhibition also interferes with virulence-related traits in C. albicans, including the secretion of degradative enzymes and yeast-to-hypha transitioning (3,4,12,13).…”

“…The fungal vacuole, a degradative organelle roughly equivalent to the mammalian lysosome, plays an important role in numerous biological processes in C. albicans, including key aspects of pathogenesis. Previous studies have established that C. albicans mutants compromised in vacuolar function are defective in yeast-to-hypha transitioning, a major virulence-related trait, and exhibit reduced virulence in vivo (1,2).…”

“…V-ATPase is located at the vacuolar membrane and throughout the endomembrane system, including prevacuolar compartments and the Golgi complex (1). The acidification of these organelles has several important functions: first, the protons pumped into the compartment by V-ATPase energize multiple secondary transporter systems, such as those involved in metal ion homeostasis, and second, the acidic pH created by V-ATPase is necessary for the activity of degradative enzymes.…”

“…The acidification of these organelles has several important functions: first, the protons pumped into the compartment by V-ATPase energize multiple secondary transporter systems, such as those involved in metal ion homeostasis, and second, the acidic pH created by V-ATPase is necessary for the activity of degradative enzymes. Accordingly, in both Saccharomyces cerevisiae and C. albicans, mutations in VATPase lead to the Vma Ϫ phenotype, which is characterized by poor growth at alkaline pH as well as defective metal sequestration, glycerol metabolism, and other responses to environmental stress conditions (1,(3)(4)(5)(6). V-ATPase mutants are also impaired in vacuolar biogenesis due to defects in both vacuolar membrane fusion and fission (7).…”

“…V-ATPase is composed of two multisubunit domains, V o and V 1 . V o is embedded in the organellar membrane and is the site of proton transport.…”