Solution structure of human insulin-like growthfactor II. Relationship to receptor and binding protein interactions

Allan M. Torres, Briony E. Forbes, Sally E. Aplin, John C. Wallace, Geoffrey L. Francise, Raymond S. Norton

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Abstract

The three-dimensional structure of human insulin-like growth factor (IGF) II in aqueous solution at pH 3.1 and 300 K has been determined from nuclear magnetic resonance data and restrained molecular dynamics calculations. Structural constraints consisting of 502 NOE-derived distance constraints, 11 dihedral angle restraints, and three disulfide bridges were used as input for distance geometry calculations in DIANA and X-PLOR, followed by simulated annealing refinement and energy minimization in X-PLOR. The resulting family of 20 structures was well defined in the regions of residues 5 to 28 and 41 to 62, with an average pairwise root-mean-square deviation of 1.24 Å for the backbone heavy-atoms (N, C*, C) and 1.90 Å for all heavy atoms. The poorly defined regions consist of the N and C termini, part of the B-domain, and the C-domain loop. Resonances from these regions of the protein gave stronger cross peaks in two dimensional NMR spectra, consistent with significant motional averaging. The main secondary structure elements in IGF-II are α-helices encompassing residues 11 to 21, 42 to 49 and 53 to 59. A small anti-parallel β-sheet is formed by residues 59 to 61 and 25 to 27, while residues 26 to 28 appear to participate in intermolecular β-sheet formation. The structure of IGF-II in the well-defined regions is very similar to those of the corresponding regions of insulin and IGF-I. Significant differences between IGF-II and IGF-I occur near the start of the third helix, in a region known to modulate affinity for the type 2 IGF receptor, and at the C terminus. The IGF II structure is discussed in relation to its binding sites for the insulin and IGF receptors and the IGF binding proteins.

Original languageEnglish
Pages (from-to)385-401
Number of pages17
JournalJournal of Molecular Biology
Volume248
Issue number2
Publication statusPublished - 1995
Externally publishedYes

Keywords

  • Distance geometry
  • Growth factor
  • Moleculardynamics
  • NMR
  • Protein structure

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