Malaria is a severe disease causing significant morbidity and mortality. The disease is caused by the Plasmodium species of parasites that belong to the phylum Apicomplexa. Transmission of the parasite requires the completion of its life cycle in the mosquito involving the invasion of salivary glands. MAEBL is a chimeric protein present in the micronemes of sporozoites that invade salivary glands and has been shown to be essential to invasion. My hypothesis is that successful invasion of salivary glands requires the recognition of a specific receptor by MAEBL on salivary glands. We expect that this recognition is dependent on interactions with glycosaminoglycans and conformation of the ligand domain M2 of MAEBL, which is a domain, rich in cysteines and other residues typically important for 3D structure. The aims of my research are: 1) To gain insights into the structure of ligand domain M2 and to determine its function of in the invasion of mosquito salivary glands, 2) To study the role of glycosaminoglycans in MAEBL ligand-receptor interactions.
To understand the function of MAEBL ligand domains in the invasion of mosquito salivary glands, the ligand domain M2, and the subdomains of M2, M2sd1 and M2sd2 were cloned and expressed in the BL21(DE3)pLysE strain of E.coli. Refolded, recombinant proteins were analyzed by LC-MS/MS mass spectrometry. We performed binding assays using these recombinant proteins with Anopheles stephensi salivary glands. Our results showed that refolded, recombinant, ligand domain M2 binds to mosquito salivary glands, while reduced and alkylated protein fails to bind. MAEBL ligand domain binding was dependent on a protease-sensitive epitope. Additional analysis using a panel of sulfated glycosaminoglycans suggested an essential role for these molecules in receptor recognition.