These proteins define the parasite and its special life style and distinguishes it from other organisms and their often already well-studied processes. As an example, the parasite modifies the host cell it grows in by exporting several hundred different kinds of its proteins. These proteins take over and in effect turn the host red blood cell into a hybrid consisting of both, host and parasite proteins. This is important for the parasite to survive and proliferate in the intracellular environment. Most other cells face a very different environment and lack this aspect in their biology. The situation of the parasite is even different from most other intracellular pathogens, because the red blood cell is highly specialised and has lost all its organelles, presenting the parasite with unique challenges to be solved as well as advantages to be exploited (e.g. to hide from the host's immune system).
Our rationale for identifying and studying such parasite-specific processes is two fold:
- Firstly, they present unique and exciting cell biology with novel biological principles outside of the well-known and most-studied housekeeping functions. Understanding these processes will explain how the parasite interacts with its host cell to survive in its unique environment. It also permits us to link highly derived proteins (proteins that have evolved to such an extent that they are not recognisable anymore), with existing processes and known functions and also provides information on the evolution of proteins.
- Secondly, anything differing from processes occurring in the host represents a good drug target, because chemotherapeutic inhibition of these processes is less likely to harm the host. Hence, down the track, these processes are expected to become drug targets.
To achieve our goals we use open as well as focussed approaches:
to find/use parasite proteins involved in already known parasite-specific essential processes (or processes containing parasite-specific aspects) and understanding how this toolbox of proteins brings about these processes. Topics qualifying for this that we study include:
- Endocytosis (the vesicle-mediated large scale uptake of host cell cytosol by the parasite) and its relevance for resistance of the parasite to the current frontline antimalarial drug Artemisinin
- In relation to endocytosis, the parasite-specific aspects of general vesicular trafficking, i.e. how proteins and other cargo are correctly distributed to their target destination in the cell
- Functions of the membrane barrier separating the parasite from the host cell (the parasitophorous vacuolar membrane that corresponds to the parasite-host cell interface) and its proteins
- Protein export and function of host cell modifications for the parasite
systematic (unbiased) quest to identify and functionally analyse proteins unique for malaria parasites to uncover novel parasite biology. We do this by conducting screens to identify such proteins followed by functional analyses. We also determine with which other proteins these targets interact to link them to other such proteins or known processes.
To address these questions we developed genetic tools that permit us to conditionally inactivate parasite proteins and monitor the consequences using a range of assays (including for instance various microscopy techniques such as 3D imaging over time). In addition we use interaction analyses, including a novel version of BioID we term DiQ-BioID, to identify the proteins involved in these processes. With this toolbox a single genomically modified cell line per target protein permits physiological localisation of the target in the cell, its rapid inactivation and to identify its interactors. This makes possible to identify the proteins involved in key processes specific for the parasite and determine how the involved proteins function mechanistically.