title: Characterisation of urea-denatured states of an immunoglobulin superfamily domain by heteronuclear NMR.
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.
authors.affiliation: Cambridge Centre for Protein Engineering, University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, U.K.
authors.forename: S
authors.initials: S
authors.lastname: Fong
authors.forename: M
authors.initials: M
authors.lastname: Bycroft
authors.forename: J
authors.initials: J
authors.lastname: Clarke
authors.forename: S M
authors.initials: SM
authors.lastname: Freund
mesh_terms: D007136:Immunoglobulins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000295:instrumentation*; D011489:Protein Denaturation; D014508:Urea
chemical_list: D007136:Immunoglobulins; D014508:Urea