The parasite Leishmania causes leishmaniasis, which is a spectrum of diseases ranging in severity from a skin ulcer to fatal visceral disease. Currently, there are no vaccines against leishmaniasis and chemotherapy is really the only means of treatment. Leishmania is known to synthesize a range of mannose-rich glycoconjugates called phosphoglycans that form the cell surface or that are secreted; these are the molecules involved in infectivity and survival of the Leishmania parasite inside human macrophages. Of the glycoconjugates produced by Leishmania several of these molecules are considered virulence factors, and parasites lacking them are viable but cannot survive in macrophages or mice and their biosynthesis depends directly or indirectly on the availability of GDP-mannose. Despite the fact that the virulence factors are considered excellent antimicrobial drug targets, the investigation of the mannose activation pathway as a potential target for anti-Leishmania drug development has not been addressed. Therefore, novel drugs targeting the enzymes GDP-mannose pyrophosphorylase (GDP-MP) and phosphomannomutase (PMM) in the biosynthetic pathway for the glycoconjugate GDP-mannose will be explored. The data from the recently reported crystal structure of PMM from Leishmania mexicana is expected to be similar to other forms of leishmaniasis because of the high degree of similarity between the genes in different Leishmania species. Dr. Emanuela Handman in the Infection and Immunity Division of The Walter and Eliza Hall Institute (WEHI) of Medical Research is set to conduct a high throughput screen of a 100,000 compound library of small molecules in collaboration with Dr. Ian Street (Structural Biology Division at WEHI), which will lead to potential """"""""hit"""""""" compounds. Compounds that exhibit confirmed inhibitory activity in the primary screen will be tested in a counter assay designed to detect those compounds that have produced """"""""false positives."""""""" These key compounds will then be subjected to docking experiments and in silico screening for inhibitors using three-dimensional structures. These docking studies will be conducted on the closed form of the enzyme that is observed after binding to the drug, but the open form will also be probed for other potential inhibitor binding sites. Dr. Jonathan Baell's research group in the Medicinal Chemistry Division at WEHI will synthesize the identified initial target compounds. Relevance: Leishmania cause a spectrum of diseases ranging in severity from self-healing skin lesions to fatal visceral disease, collectively known as leishmaniases. The WHO has classified leishmaniasis as a category 1 disease, i.e. emerging and uncontrolled. ? ? ?
