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Solution structures of human myeloma IgG3 antibody reveal extended Fab and Fc regions relative to the other IgG subclasses

DOI: 10.1016/j.jbc.2021.100995 DOI Help

Authors: Valentina A. Spiteri (University College London (UCL)) , Margaret Goodall (University of Birmingham) , James Doutch (ISIS Facility) , Robert P. Rambo (Diamond Light Source) , Jayesh Gor (University College London) , Stephen J. Perkins (University College London (UCL))
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Biological Chemistry , VOL 40

State: Published (Approved)
Published: July 2021

Open Access Open Access

Abstract: Human immunoglobulin IgG3 possesses a uniquely long hinge region that separates its Fab antigen-binding and Fc receptor-binding regions. Owing to this hinge length, the molecular structure of full-length IgG3 remains elusive, and the role of the two conserved glycosylation sites in the Fc region is unknown. To address these issues, we subjected glycosylated and deglycosylated human myeloma IgG3 to multidisciplinary solution structure studies. Using analytical ultracentrifugation, the elongated structure of IgG3 was determined from the reduced sedimentation coefficients s020,w of 5.82-6.29 S for both glycosylated and deglycosylated IgG3. X-ray and neutron scattering showed that the Guinier RG values were 6.95 nm for glycosylated IgG3 and were unchanged after deglycosylation, again indicating an elongated structure. The distance distribution function P(r) of both forms of IgG3 showed a maximum length of 25-28 nm and three distinct maxima. The molecular structure of IgG3 was determined using atomistic modelling based on molecular dynamics simulations of the IgG3 hinge and Monte Carlo simulations to identify physically-realistic arrangements of the Fab and Fc regions. This resulted in libraries containing 135,135 and 73,905 glycosylated and deglycosylated IgG3 structures respectively. Comparisons with the X-ray and neutron scattering curves gave 100 best-fit models for each of the two forms of IgG3 that accounted for the experimental scattering curves. These models revealed the first molecular structures for full-length IgG3. The structures exhibited relatively-restricted Fab and Fc conformations joined by an extended semi-rigid hinge, which explains the potent effector functions of IgG3 relative to the other subclasses IgG1, IgG2 and IgG4.

Journal Keywords: Analytical ultracentrifugation; antibody modelling; small-angle neutron scattering; human IgG subclasses; small angle X-ray scattering

Subject Areas: Biology and Bio-materials, Chemistry

Instruments: B21-High Throughput SAXS

Added On: 26/07/2021 13:13


Discipline Tags:

Biochemistry Chemistry Structural biology Life Sciences & Biotech

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)