Disulfide-bridged proteins with potential for medical applications: therapeutic relevance, sample preparation and structure - function relationships

A variety of proteins with potential for medical applications contain disulfide-bridges. In this review, the author describes investigations of such proteins, particularly those concerned with clarification of structure – function relationships and molecular engineering, focusing on three classes of targets, namely human lysozyme, plant lectins composed of hevein-type domains and extracellular domains of human Fas ligand and Fas receptor. With each class of proteins, biological functions relevant to therapeutic applications, structural features, development of sample preparation methods and the experimental results for the clarification of structure – function relationships, including those of protein engineering studies on the basis of their three-dimensional structures, is summarized in the light of our current knowledge. The studies were performed by elucidating details in structural and functional consequences after introducing ligand complex formations, site-directed mutagenesis and site-specific chemical modifications, which employed various biochemical and biophysical analyses in combination with newly developed recombinant expression and chemical synthesis methods. The main findings from the studies include basic principles concerning the structure – function relationships in the enzymatic catalysis by endoglycosidases and carbohydrate recognition by lectins as well as biotechnological advances in the use of extracellular domains of death ligands and death receptors. The experimental results reviewed here will contribute to the future development of novel disulfide-bridged proteins with therapeutic usefulness targeting unmet medical needs.