Protist parasites, such as Plasmodium spp. and Leishmania spp., cause tremendous problems worldwide and have enormous health, social and economic impacts. Membrane bound pyrophosphatases (mPPases), enzymes that couple the pyrophosphate cleavage to the transport of proton/sodium ion across membranes, occur in these parasites but not in humans. These enzymes are located in the acidocalcisomes, an acidic electron-dense organelle rich in polyphosphates and calcium ions. Due to their importance for the parasites viability and infectivity, mPPases are validated drug targets for treating diseases caused by them.
In the Goldman Lab, we are working to understand the detailed structure and mechanism of these enzymes and their inhibition by drug-like compounds. This is being achieved through X-ray crystallography, enzymatic and ion pumping activity assays, and small molecule screening in vitro and in Plasmodium falciparum. We work closely with Prof. Yli-Kauhaluoma, Dr. Xhaard, and Prof. Meri.
Apart from mPPases, we are also working on other proteins to understand the phosphate sensing mechanism and regulation in the acidocalcisomes of protist parasites. This involves several soluble and membrane proteins, e.g. soluble pyrophosphates, vacuolar transporter chaperon (VTC) complex, inositol 1,4,5-triphosphate receptor and Na:Phosphate symporter. These proteins are essential for the survival, virulence, and infectivity of the parasites which makes them other good candidates for drug targets. We have established the CRISPR/Cas9 method for genomic protein tagging in Leishmania tarentolae which will be used for structure determination of proteins isolated directly from their endogenous source by cryoEM and for functional studies.
We have also started focussing again on the RET tyrosine kinase, a project that began many years ago in my lab in collaboration with Prof. Mart Saarma. In this project, our focus is on understanding the full structure, from outside ligand binding to inside signalling, and connecting that to specific genetic diseases. There are, indeed, no full models of the signalling mechanisms of any tyrosine kinase receptor. This work is spearheaded by my graduate student Sadegh Bekverdi.
Mimmu Hiltunen, my senior graduate student, drives a project on the protein PTCHD1, which she has shown to be a cholesterol transporter. Unlike the closely-related PTCH1, it is not involved in hedgehog signalling. Mutations in PTCHD1 are commonly found in people who fall on the spectrum, and we wish to understand the connections between structure, function, and neurochemistry. PTCHD1 and protien affected in Fragile X (FMRP) also seem to share a biological network. On this we collaborate with Prof. Maija Castrén at the University of Helsinki, with Profs Paul Hamel and John Vincent at the University of Toronto, and with Dr. Natalia Riobo-Del Galdo at the University of Leeds.
The EU doctoral network, StraDiVarious, which I head will focus on a long-standing interest of mine, proteins on bacterial surfaces, such as the trimeric autotransporters.