Bent domain structure of recombinant human IgE-Fc in solution by X-ray and neutron scattering in conjunction with an automated curve fitting procedure.
Human immunoglobulin E (IgE) consists of 14 domains, each with the characteristic immunoglobulin fold structure. Compared with the 12-domain structure of immunoglobulin G (IgG), IgE has an additional pair of domains (C epsilon 2) in the Fc region in place of the hinge of IgG. The crystal structure of the 4-domain Fc fragment of IgG is known, but not that of the 6-domain Fc fragment of IgE (IgE-Fc). In order to elucidate the position of the C epsilon 2 domains in the domain structure of IgE-Fc, IgE-Fc was studied by synchrotron X-ray and pulsed neutron scattering. The upper limit on the X-ray radius of gyration RG which determines macromolecular elongation was determined to be 3.52 +/- 0.14 nm. That for the neutron RG (measured in 100% 2H2O buffers) was 3.53 +/- 0.05 nm. The X-ray and neutron cross-sectional radii of gyration were 1.89 +/- 0.05 and 1.56 +/- 0.09 nm, respectively. The scattering curves were modeled on the basis of a previously-predicted model for IgE-Fc (Helm, B. A., Ling, Y., Teale, C., Padlan, E. A., & Brüggemann, M. (1991) Eur. J. Immunol. 21, 1543-1548). The extended arrangement of domains in that model resulted in poor agreement with experimental data. Interactive and automated procedures for the fitting of crystallographically-derived domain models to scattering data were developed. Each pair of C epsilon 2, C epsilon 3, and C epsilon 4 domains was translated and rotated relative to the remaining structure in a comprehensive five-parameter search of more than 37,000 models. Substantially improved agreement between the experimental and calculated scattering curves was obtained. Bent models for IgE-Fc in which the C epsilon 2 domain pair is rotated by at least 40-50 degrees from its position in the previously predicted linear IgE model consistently gave the best agreement with the X-ray and neutron scattering curves. Such a structure for the Fc fragment accounts in part for the bent structure previously proposed for intact human IgE, which is important for understanding the interaction between IgE and its receptors.
Beavil
A J
AJ
Randall Institute, King's College London, U.K.
Young
R J
RJ
Sutton
B J
BJ
Perkins
S J
SJ
D003198:Computer Simulation; D018360:Crystallography, X-Ray; D006801:Humans; D007073:Immunoglobulin E / Q000737:chemistry*; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry*; D008958:Models, Molecular; D009502:Neutrons; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry
D007141:Immunoglobulin Fc Fragments; D011994:Recombinant Proteins; D007073:Immunoglobulin E