title: Structure and dynamics of des-pentapeptide-insulin in solution: the molten-globule hypothesis.
abstract: Structures of insulin in different crystal forms exhibit significant local and nonlocal differences, including correlated displacement of elements of secondary structure. Here we describe the solution structure and dynamics of a monomeric insulin analogue, des-pentapeptide-(B26-B30)-insulin (DPI), as determined by two-dimensional NMR spectroscopy and distance geometry/restrained molecular dynamics (DG/RMD). Although the solution structure of DPI exhibits a general similarity to its crystal structure, individual DG/RMD structures in the NMR ensemble differ by rigid-body displacements of alpha-helices that span the range of different crystal forms. These results suggest that DPI exists as a partially folded state formed by coalescence of distinct alpha-helix-associated microdomains. The physical reality of this model is investigated by comparison of the observed two-dimensional nuclear Overhauser enhancement (NOE) spectroscopy (NOESY) spectrum with that predicted from crystal and DG/RMD structures. The observed NOESY spectrum contains fewer tertiary contacts than predicted by any single simulation, but it matches their shared features; such "ensemble correspondence" is likely to reflect the effect of protein dynamics on observed NOE intensities. We propose (i) that the folded state of DPI is analogous to that of a compact protein-folding intermediate rather than a conventional native state and (ii) that the molten state is the biologically active species. This proposal (the molten-globule hypothesis) leads to testable thermodynamic predictions and has general implications for protein design.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
authors.forename: Q X
authors.initials: QX
authors.lastname: Hua
authors.forename: M
authors.initials: M
authors.lastname: Kochoyan
authors.forename: M A
authors.initials: MA
authors.lastname: Weiss
mesh_terms: D002151:Calorimetry; D004220:Disulfides; D007328:Insulin / Q000031:analogs & derivatives* / Q000737:chemistry; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D011487:Protein Conformation; D012996:Solutions; D013816:Thermodynamics; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D004220:Disulfides; D007328:Insulin; D046911:Macromolecular Substances; D012996:Solutions; C007285:insulin, despentapeptide(B26-B30)-