Characterisation of urea-denatured states of an immunoglobulin superfamily domain by heteronuclear NMR

J Mol Biol. 1998 May 1;278(2):417-29. doi: 10.1006/jmbi.1998.1702.

Abstract

The structural and dynamic properties of an immunoglobulin superfamily domain (IgSF), Ig 18', have been characterised by NMR at 285 K, in the presence of 4.2 M and 6.0 M urea, respectively. Analysis of chemical shift deviations, 3JHNHalpha coupling constants, sequential NOE pattern, and 15N relaxation data reveals that although the two urea-denatured states are highly disordered, some local turn-like residual structures do exist. Moreover, some distinct differences between the properties of the two denatured states are observed. In 4.2 M urea-denatured Ig 18', regions 80-83 and 86-92 adopt turn-like conformations, furthermore, region 84-93 is involved in slow exchange processes that occur on a micro- to millisecond time-scale. In the 6.0 M urea-denatured state, these turn-like conformations are less occupied, and chemical exchange processes in region 84-93 are largely reduced. In contrast, region 32-36 has persistent turn-like structures in both urea-denatured states. Some correlation between the spectral density function at 0 frequency, Jeff(0), for the urea-denatured states and the secondary structure elements of the folded state have been observed. Except for the terminal regions, residues corresponding to beta-strands have higher Jeff(0) values compared to residues corresponding to loops. The characterisation and comparison of the two urea-denatured states highlight residues that possess properties that may be crucial for the initiation of folding of this domain.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Immunoglobulins / chemistry*
  • Immunoglobulins / metabolism
  • Models, Molecular
  • Nuclear Magnetic Resonance, Biomolecular / instrumentation*
  • Protein Denaturation
  • Urea*

Substances

  • Immunoglobulins
  • Urea