Molecular recognition in protein-protein interactive sites, design of peptide, peptidomimetic and other biologic active site-directed mono- and bifunctional agents.
Our interest is in the development of a molecular level understanding of how one protein recognizes and binds to another. Wehopetobeabletotranslatethisknowledgeinto the effective design of small molecules which mimic the structure of one of the interacting proteins. This accomplishment would represent a fundamental advance in drug design and would further allow us to manipulate specific protein-protein interactions, and thus to define their role in biology. Complex biological systems are general Iy controlled through selective protein-protein interaction. The excessive formation of a particular protein-protein complex may be responsible for an abnormality recognized as a disease. To control the extent to which specificprotein-proteincomplexes are formed we need to understand the molecular basis for their formation.
Currently there are two major problems which occupy our interest: (1 ) How does the immunoregulatory cytokine, interleukin-1, interact with its receptor, and (2) How do the curarimimetic neurotoxins block the nicotinic acetylcholine receptor. Both of these systems are representative of very strong non covalent interactions between structurally well defined protein ligands (neurotoxin and interleukin-1 ) and their protein cellular receptors, which are less well defined structurally.
We have taken two basic approaches to defining the structural interaction in such complexes. First, from x-ray structural information available for interleukin-1, and from the inhibitory character of synthetic linear peptides based on the structure of interleukin-1, we are beginning to define the interfacial recognition site between interleukin-1 and its receptor. Interleukin-1 is a 172 amino acid length polypeptide folded into the approximate shape of a tetrahedron. It is the carboxyterminal 33 amino acids, occupying a portion of one of the faces of the tetrahedron, which appears to provide most of the basis for the recognition of interleukin-1 by its receptor. This information should lead us inthedirection ofthesynthesis of small constrained polypeptides and eventually nonpeptides which will bind tightly to interleukin-1. Selective competitive inhibitors of interleukin-1 would be expected to have considerable application as selective immunosuppressive agents.
In the study of the interaction between curarimimetic neurotoxins and acetylcholine receptors we have taken a similar approach and this has resulted in the definition of the general features of the binding interaction and in the synthesis of conformationally constrained peptides which are good inhibitors of neurotoxin binding. In addition, we have developed a number of novel heterobifunctional agents which have been useful in defining the details of the toxin-receptor interaction. The reagents may also be useful in defining other protein-protein interactions.
While some of our chemical approaches to defining heterobifunctional agents have not been useful in defining protein-protein action of interest to us, we are developing some reagents with novel mechanisms of activation at protein active sites to which they may be affinity directed. These include reversible organomercury linkages and redox sensitive agents activated through protein mediated oxidation reactions, which may also feature rapid covalent reactions between reagent and protein subsequent to the initial redox reaction. These studies have led to affinity dependent hydroxycatechol redox active agents.