Protein crystallography and infectious diseases

Abstract

The current rapid growth in the number of known 3-dimensional protein structures is producing a database of structures that is increasingly useful as a starting point for the development of new medically relevant molecules such as drugs, therapeutic proteins, and vaccines. This development is beautifully illustrated in the recent book, Protein structure: New approaches to disease and therapy (Perutz, 1992). There is a great and growing promise for the design of molecules for the treatment or prevention of a wide variety of diseases, an endeavor made possible by the insights derived from the structure and function of crucial proteins from pathogenic organisms and from man.We present here 2 illustrations of structure-based drug design. The first is the prospect of developing antitrypanosoma1 drugs based on crystallographic, ligand-binding, and molecular modeling studies of glycolytic glycosomal enzymes from Trypanosomatidae. These unicellular organisms are responsible for several tropical diseases, including African and American trypanosomiases, as well as various forms of leishmaniasis. Because the target enzymes are also present in the human host, this project is a pioneering study in selective design. The second illustrative case is the prospect of designing anti-cholera drugs based on detailed analysis of the structure of cholera toxin and the closely related Escherichia coli heat-labile enterotoxin. Such potential drugs can be targeted either at inhibiting the toxin's receptor binding site or at blocking the toxin's intracellular catalytic activity.Study of the Vibrio cholerae and E. coli toxins serves at the same time as an example of a general approach to structure-based vaccine design. These toxins exhibit a remarkable ability to stimulate the mucosal immune system, and early results have suggested that this property can be maintained by engineered fusion proteins based on the native toxin structure. The challenge is thus to incorporate selected epitopes from foreign pathogens into the native framework of the toxin such that crucial features of both the epitope and the toxin are maintained.That is, the modified toxin must continue to evoke a strong mucosal immune response, and this response must be directed against an epitope conformation characteristic of the original pathogen.

Bacterial Surface Association of Heat-labile Enterotoxin through Lipopolysaccharide after Secretion via the General Secretory Pathway

“…After binding, the receptor/toxin complex is internalized, and LTA is trafficked to the cytosol (13,15,16). Upon entry into the cytosol, the catalytic subunit constitutively activates adenylate cyclase, resulting in water and electrolyte efflux from the host cells (17).…”

Lipopolysaccharide 3-Deoxy-d-manno-octulosonic Acid (Kdo) Core Determines Bacterial Association of Secreted Toxins

“…After binding, the receptor/toxin complex is internalized by the host cell and the A subunit undergoes retrograde trafficking to the cytosol via the endoplasmic reticulum (ER) (6,8,9). Upon entry into the cytosol, the catalytic subunit constitutively activates adenylate cyclase, resulting in water and electrolyte efflux from the host cells (10).…”

Cloning, Expression, Purification and Characterization Of Triosephosphate Isomerase from Trypanosoma Cruzi

“…Thus, several of the enzymes of the glycolytic pathway of Trpano.wma brucei, the parasite that produces sleeping sickness in humans and nagana in cattle in Africa, have been extensively studied in both function and structure [4,. The metabolic pathways that operate in Trypnosoma cruzi, which produces Chagas disease, have also been investigated [lo], but less is known of the structure of these enzymes.…”