Final Report Summary - PARAMOTSIG (Receptor signalling mediating malaria parasite motility)
Plasmodium sporozoites are the motile forms of the malaria parasite injected into the vertebrate host by a mosquito. Sporozoites are ‘born’ in parasitic oocysts at the mosquito gut from where they need to exit to enter salivary glands. Within these glands they can reside for weeks until they are transmitted to a vertebrate host. During a mosquito bite sporozoites are deposited in the skin and need to migrate within the dermis to enter blood vessels and be transported to the liver. Sporozoites migrate at incredibly high speed, about 10 times faster than the cells of the immune system chasing after them. Once in the blood sporozoites arrest at the liver and enter hepatocytes to differentiate into thousands of progeny parasites that enter red blood cells, which ultimately causes the symptoms of malaria.
Our project aimed to get a better insight into Plasmodium sporozoite motility using a combination of microscopy, biophysical studies and genetically modified parasites. In order to move at their high speed, sporozoites rely on proteins at their surface and a motor machinery that resides under the plasma membrane. The project brought advances in our understanding of sporozoite motility on the molecular and biophysical level. In order to move sporozoites secrete the surface proteins at their front end. It was assumed that these link to the substrate and are moved backwards by the motor machinery. We found that this rearward transport is occurring at a very fast rate, much faster than parasite forward movement. We also found that when the motor machinery was only slightly impaired the capacity of the parasite to generate force was much lower, while their capacity to migrate was still intact. This puzzling outcome is currently focus of new research. Another unexpected finding was the discovery of a role for parasite motility in sporozoite egress from oocysts. We were the first to film how sporozoites exit the oocysts in near-natural settings, to quantify the process and investigate it with different mutant parasite lines. This again now opens up a mechanistic dissection of the process of parasite egress from oocysts. We further found, surprisingly again, that the three main proteins so far thought to be involved in motility could all be deleted and the sporozoites could still move, albeit at a much reduced level. This lead to the search for new important proteins in motility and we identified and characterized three new such proteins, one being important for sporozoite egress and salivary gland invasion, the two others for salivary gland entry and all three for motility. Lastly, by dissecting the domains of the proteins as intended we unexpectedly found that one domain is completely essential for motility. I will now seek funding from the Proof-of-Concept scheme to explore this further in the context of generating motility blocking antibodies as experimental vaccines.
Our project aimed to get a better insight into Plasmodium sporozoite motility using a combination of microscopy, biophysical studies and genetically modified parasites. In order to move at their high speed, sporozoites rely on proteins at their surface and a motor machinery that resides under the plasma membrane. The project brought advances in our understanding of sporozoite motility on the molecular and biophysical level. In order to move sporozoites secrete the surface proteins at their front end. It was assumed that these link to the substrate and are moved backwards by the motor machinery. We found that this rearward transport is occurring at a very fast rate, much faster than parasite forward movement. We also found that when the motor machinery was only slightly impaired the capacity of the parasite to generate force was much lower, while their capacity to migrate was still intact. This puzzling outcome is currently focus of new research. Another unexpected finding was the discovery of a role for parasite motility in sporozoite egress from oocysts. We were the first to film how sporozoites exit the oocysts in near-natural settings, to quantify the process and investigate it with different mutant parasite lines. This again now opens up a mechanistic dissection of the process of parasite egress from oocysts. We further found, surprisingly again, that the three main proteins so far thought to be involved in motility could all be deleted and the sporozoites could still move, albeit at a much reduced level. This lead to the search for new important proteins in motility and we identified and characterized three new such proteins, one being important for sporozoite egress and salivary gland invasion, the two others for salivary gland entry and all three for motility. Lastly, by dissecting the domains of the proteins as intended we unexpectedly found that one domain is completely essential for motility. I will now seek funding from the Proof-of-Concept scheme to explore this further in the context of generating motility blocking antibodies as experimental vaccines.