The principal interest of our laboratory is the analysis of interrelationships among protein primary structure, folding and biological recognition. We have largely focused on the structure of a single small pituitary protein, neurophysin, analyzing in thermodynamic and molecular detail its interactions with the peptide hormones oxytocin and vasopressin and the complex processes that regulate its dimerization and folding. Neurophysin serves as a carrier for the hormones within the pituitary and shares common biosynthetic precursors with the hormones. Mutations in neurophysin are associated with defects in vasopressin production, leading to the disease diabetes insipidus. The availability of crystal structures and a bacterial system for the expression of designed mutant neurophysins and neurophysin precursors play central roles in experimental design and analysis.
EXAMPLES OF CURRENT RESEARCH:
1. What factors influence protein dimerization? Protein self-association phenomena play important biological roles in normal and pathological states, but the conformational factors associated with these processes are inadequately understood. In the case of neurophysin, dimerization is markedly altered by factors distant from the monomer-monomer interface, such as hormone-binding, chemical modification of a single residue or deletion of a few amino-terminal residues. We are exploring the mechanisms involved in these phenomena by analyzing the effects of site-directed mutagenesis on dimerization.
2. How do multi-domain proteins fold? Neurophysin contains two homologous domains that interact in the folded state. The extent to which folding is dependent on inter-domain interactions is being studied by comparison of the folding of the whole protein with that of isolated domains and segments of domains.
3. How do mutations in neurophysin lead to defects in vasopressin production? The importance of neurophysin to hormone production lies in its role in the correct targeting of hormone to regulated neurosecretory granules. The nature of this role, and the mechanism by which mutations impair neurophysin function, are under investigation. Neurophysins and neurophysin precursors containing mutations associated with diabetes insipidus are prepared by recombinant DNA technology and their folding and functional properties analyzed.