Abstract
Plasmodium falciparum invades erythrocytes and extensively modifies them in a manner that increases the virulence of this malaria parasite. A single heat-shock 70 kDa-type chaperone, PfHsp70-x, is among the parasite proteins exported to the host cell. PfHsp70-x assists in the formation of a key protein complex that underpins parasite virulence and supports parasite growth during febrile episodes. Previous work resolved the crystallographic structures of the PfHsp70-x ATPase and substrate-binding domains, and showed them to be highly similar to those of their human counterparts. Here, 233 chemical fragments were screened for binding to the PfHsp70-x ATPase domain, resulting in three crystallographic structures of this domain in complex with ligands. Two binding sites were identified, with most ligands binding proximal to the ATPase nucleotide-binding pocket. Although amino acids participating in direct ligand interactions are conserved between the parasite and human erythrocytic chaperones, one nonconserved residue is also present near the ligand. This work suggests that PfHsp70-x features binding sites that may be exploitable by small-molecule ligands towards the specific inhibition of the parasite chaperone.
Highlights
Over 400 000 deaths are attributed to malaria each year, primarily in sub-Saharan Africa and among children under the age of five years (World Health Organization, 2019)
Using the fragmentscreening pipeline established in the XChem laboratory at Diamond Light Source, we incubated these crystals with 233 chemical fragments from the DSI-poised (Cox et al, 2016) and FragLite (Wood et al, 2019) libraries and performed X-ray diffraction experiments (Supplementary Table S1)
The overall $40% attrition rate of crystals that did not yield useful data could in large part be attributed to the incubation process itself, which exposes the crystals to dimethyl sulfoxide (DMSO); preliminary experiments had shown that $25% of crystals handled had worsened diffraction characteristics
Summary
Over 400 000 deaths are attributed to malaria each year, primarily in sub-Saharan Africa and among children under the age of five years (World Health Organization, 2019). The parasite exports a complement of nearly 500 proteins to the host cell (Spillman et al, 2015; Warncke et al, 2016; Proellocks et al, 2016; de Koning-Ward et al, 2016), among which is the adhesion ligand P. falciparum erythrocyte membrane protein 1 (PfEMP1; Hviid & Jensen, 2015). Cytoadhesion and rosetting are beneficial to the parasite as they allow the avoidance of splenic passage, where parasitized erythrocytes may be recognized and destroyed, thereby enhancing parasite growth.
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