Research in Dr. Hol's group is multi-disciplinary and directed towards the structure determination of exciting protein molecules as a starting point for understanding the way they function and resolving the intricacies of their often miraculous architecture. Designing new inhibitors that can be further developed into drugs, in particular for the treatment of infectious tropical diseases.
The studies in the last ten years have focused on unraveling the crystal structures of key proteins from major tropical pathogens in parallel with structure-based development of inhibitors of these proteins. Examples are:
- We have made good progress in deciphering the mode of action of cholera toxin and developing high affinity receptor binding antagonists. The structure of the fully activated form of the toxin, in complex with the human G-protein ARF6, has also been obtained recently. Ongoing studies are aimed at understanding additional interactions of the toxin with human proteins.
- Structures of five proteins from the sophisticated Type II Secretion System of Vibrio cholerae, which translocates cholera toxin across the outer membrane, have been unraveled in recent years. These are actually only initial steps in understanding the mode of action of this fascinating, two-membrane-spanning, molecular machinery.
- The intriguing RNA-editing editosome of the sleeping sickness parasite Trypanosoma brucei is able to incorporate dozens of nucleotides into immature mRNAs, resulting in mature messages which are sometimes twice the size of the starting mRNA. The three-dimensional structures of two editosome key enzymes have recently been solved at high resolution revealing fully their nucleotide binding modes. Structure determinations of multiple editosome sub-complexes and complexes with RNA are currently being undertaken.
- Another most unusual feature of Trypanosoma brucei and related tropical pathogens is the presence of "glycosomes", unique organelles that are critical for energy generation in the bloodstream form of the sleeping sickness parasites. We are studying the "peroxins", proteins responsible for the biogenisis of these essential organelles.
- The major human malaria parasites Plasmodium falciparum and P. vivax are able to enter human liver cells as well as erythrocytes. The proteins involved in the "invasion machinery" are only just being discovered. We have solved the three-dimensional structure of a key interaction between two proteins of this cell invasion machinery. These are obviously important drug targets for new anti-malarials. Studies on other critical components of this dynamic macromolecular machinery are under way.
- Two key DNA regulators of Mycobacterium tuberculosis have been caught in the act of binding DNA, which is exploited for the design of small-molecule deregulators of these regulators. One of these regulators shows totally unexpected large variations in tertiary and quaternary structure during its course of action.
Several contributions have also been made to the development of methods in protein crystallography. Most recently these have been made largely within the framework of the Structural Genomics of Pathogenic Protozoa (SGPP) Consortium that has expressed thousands of genes from trypanosomatid and Plasmodium species, purified hundreds of proteins from these pathogens, and solved dozens of crystal structures. Progress can be seen on the SGPP website. This project is being continued as the Medical Structural Genomics of Pathogenic Protozoa (MSGPP) Program Project.