Our research projects
Our group works with the organism causing the severest form of human malaria, the protozoan parasite Plasmodium falciparum. This parasite has a complex life cycle involving a mosquito and a human host. The symptoms of the disease are due only to one particular part of this life cycle, the development of P. falciparum parasites inside of human red blood cells. In this phase the parasite goes through continuously repeating replication cycles in the red blood cell, leading to an exponential multiplication of parasite numbers in the host. Each of these 48 hour cycles involves invasion of the parasite into a red blood cell, growth of the parasite, replication of the parasite and finally - causing the destruction of the host cell - release of up to 32 daughter parasites that invade new red blood cell. This is blood cycle is what we study in our laboratory.
Our key interest is to identify and understand processes that take place during parasite development in the red blood cell that are unique to the biology of malaria parasites and do not exist in other organisms. As in all organisms, the functions of the parasite cell are carried out by proteins that derived from blueprints encoded in the cells genome (the genes). The proteins act as small machines and building blocks that work together to make an intricately complex bigger machine (the cell). The proteins ensure that the cell can survive and divide (e.g. by using smaller molecules such as sugars as an energy source; using amino acids to build proteins; synthesising DNA to replicate the genome; mediating cell motility; sensing and interacting with the environment the cell finds itself in etc). Many of these processes are so called 'housekeeping' functions that exist in the cells of most organisms such as the energy metabolism, structural components, or making DNA. In different organisms these functions are carried out by evolutionary related proteins that can usually be identified by their similarity to each other.
However, more than a third of all proteins of P. falciparum parasites show no resemblance to any of these components found in other organisms, representing biology unique to this parasite.
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:
Focussed approach:
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
Open approach:
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.
Methodology:
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.
