W0309

Protein Crystallography in Drug Design: Tropical Diseases and Human Topisomerase I. Wim G.J. Hol, Departments of Biological Structure and Biochemistry, Howard Hughes Medical Institute and Biomolecular Structure Center, University of Washington, Seattle, WA 98195-7742

Structure-based drug design can be quite different from case to case dependent on the protein targeted, the location of the drug target protein in host and/or pathogen, the flexibility of the target protein upon ligand binding, and the nature of the site to which compounds have to bind.

One of the examples which will be discussed is cholera toxin and related AB5 heterohexamer, i.e. toxins. Two entirely different target areas have been explored so far - one a hydrophilic pentasaccharide receptor binding site which can be tackled with compounds which need not be able to cross any membrane. Water molecules play an important role in ligand binding at this site. A second area is a hydrophobic patch of the B-pentamer which interacts with the A subunit. The goal is to prevent assembly of the holotoxinin the periplasm of the toxin secreting bacteria. Some intriguing crystallographic results following up a pharmacophore search will be discussed.

Glycolytic enzymes are crucial for energy metabolism in certain stages of the life cycle of trypanosomal and malarial parasites. Results will be presented where ligands cause dramatic conformational changes in the protein, most notably in the case of phosphoglycerate kinase. The drawbacks and opportunities of this flexibility for the design selective inhibitors will be considered. In the case of glyceraldehyde-3-phosphate dehydrogenase the affinity of the lead compound adenosine would be improved by a factor of 105 due to multiple substitutions. The eventual drugs will require excellent bioavailability and have to cross several membranes when used orally.

The structure of human topoisomerase I will be highlighted and discussed in view of the most unusual mode of action of the anti-cancer drug camptothecin, discovered decades ago.

I would like to thank numerous group members, colleagues, and collaborators, for their tremendous dedication and enthusiasm for these projects.