UCLA

The complexity and breadth of the host-cell remodeling machinery in the malaria parasite P. falciparum make it a rich and exciting system for the study of host-pathogen interfaces, particularly as many of the molecular mechanisms underlying this parasite’s ability to hijack human red blood cells remain unclear. Furthermore, the P. falciparum proteome has proven recalcitrant to structural and biochemical characterization using recombinant methods, making it an intriguing model system for the development of new methods that leverage recent advances in cryoEM to enable structural studies of previously intractable systems at near-atomic resolution. The work presented here makes significant contributions in both these regards.

First, we use a targeted, CRISPR-enabled “top down” approach to determine near-atomic resolution structures of the unique malaria parasite translocon PTEX, which we purified directly from P. falciparum parasites in multiple functional states, yielding the first near-atomic resolution cryoEM structures of a protein isolated directly from an endogenous source using an epitope tag inserted into the endogenous locus with CRISPR-Cas9 gene editing.

We then developed a “bottom up” endogenous structural proteomics method whereby protein complexes enriched directly from the cellular milieu are identified by imaging and structure determination using cryoEM and mass spectrometry. As a proof of principle, we successfully used this approach to obtain near-atomic resolution structures of multiple protein complexes from the P. falciparum proteome, which has previously proven recalcitrant to expression in recombinant systems, precluding structure determination by X-ray crystallography or NMR.

The body of work described here addresses a known need for methods that overcome the limitations of structural biology approaches that depend on recombinant systems, opening the door for high resolution structure determination of a vast number of previously intractable biological systems.