Violacein-Induced Chaperone System Collapse Underlies Multistage Antiplasmodial Activity

Abstract

Antimalarial drugs with novel modes of action and wide therapeutic potential are needed to pave the way for malaria eradication. Violacein is a natural compound known for its biological activity against cancer cells and several pathogens, including the malaria parasite, Plasmodium falciparum (Pf). Herein, using chemical genomic profiling (CGP), we found that violacein affects protein homeostasis. Mechanistically, violacein binds Pf chaperones, Pf Hsp90 and Pf Hsp70-1, compromising the latter’s ATPase and chaperone activities. Additionally, violacein-treated parasites exhibited increased protein unfolding and proteasomal degradation. The uncoupling of the parasite stress response reflects the multistage growth inhibitory effect promoted by violacein. Despite evidence of proteotoxic stress, violacein did not inhibit global protein synthesis via UPR activation—a process that is highly dependent on chaperones, in agreement with the notion of a violacein-induced proteostasis collapse. Our data highlight the importance of a functioning chaperone–proteasome system for parasite development and differentiation. Thus, a violacein-like small molecule might provide a good scaffold for development of a novel probe for examining the molecular chaperone network and/or antiplasmodial drug design.

HSP70 and their co-chaperones in the human malaria parasite P. falciparum and their potential as drug targets

“…Recently, the bis-indole violacein was tested for anti-malarial properties and possible inhibitory effects on PfHSP70-1. A significant and concentration dependent inhibition of the chaperone's ATPase and aggregation suppression activity by violacein was observed (Tavella et al, 2021). Thus, the small molecule is predicted to compromise the ATP hydrolysis of PfHSP70-1 by interacting with the SBD or the SBD-NBD-interface (Tavella et al, 2021).…”

Contemporary exploitation of natural products for arthropod-borne pathogen transmission-blocking interventions

“…Besides, the bacterial isolate ( Csp _P) kills mosquito larvae by its secreted hydrogen cyanide in addition to exerting adulticidal effects [ 36 ], underscoring its broad-spectrum activity window. A related Chromobacterium species C. violaceum has been isolated from soils [ 37 ]. These bacteria produce a broad-spectrum bisindole antimalarial agent, 3-[1,2-dihydro-5-(5-hydroxy-1 H -indol-3-yl)-2-oxo-3 H -pyrrol-3-ilydeno]-1,3-dihydro-2 H -indol-2-one (violacein ( 2 )), reported to have gametocytocidal (EC 50 1.25–2.5 µM) and Plasmodium transmission-blocking activity (43% oocysts reduction) [ 37 ].…”

“…A related Chromobacterium species C. violaceum has been isolated from soils [ 37 ]. These bacteria produce a broad-spectrum bisindole antimalarial agent, 3-[1,2-dihydro-5-(5-hydroxy-1 H -indol-3-yl)-2-oxo-3 H -pyrrol-3-ilydeno]-1,3-dihydro-2 H -indol-2-one (violacein ( 2 )), reported to have gametocytocidal (EC 50 1.25–2.5 µM) and Plasmodium transmission-blocking activity (43% oocysts reduction) [ 37 ]. In another more recent study, despite pending efforts to establish the identity of anti- Plasmodium mediating molecule(s), a novel sexually inherited microsporidian MB infecting Kenyan An .…”

Inhibitors of the Plasmodium falciparum Hsp90 towards Selective Antimalarial Drug Design: The Past, Present and Future

“…Recently, design and screening for potential parasite pan-Hsp90 inhibitors are gaining attention. A promising compound, violacein, was shown to target PfHsp90 and PfHsp70, thereby abrogating the chaperone function of the molecules with promising antiplasmodial indices [ 187 ]. Since the ATP binding of PfHsp90 is closer to that of its paralogs, as they share the same Bergerat fold than to Hsp70s [ 34 ], this suggests that violacein potentially inhibits other parasite Hsp90s in eliciting its anti-plasmodial activity.…”

“…On the other hand, with high sequence similarities between Hsp90s localized in equivalent cell compartments from different species, the development of paralog-specific Hsp90 inhibitors is an attractive avenue worth exploring. As such, several Hsp90 paralog selective inhibitors have been developed [ 112 , 162 , 163 , 187 , 188 ]. These paralog selective inhibitors, if adopted to the parasitic PfHsp90_A apicoplast resident chaperone, may offer interesting possibilities, since this target is only present in apicomplexans and not in humans.…”