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Title: Solution structure and stabilities of rabbit and human IgG
Author: Rayner, L. E.
ISNI:       0000 0004 5352 2400
Awarding Body: University College London (University of London)
Current Institution: University College London (University of London)
Date of Award: 2014
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Immunoglobulin G (IgG) is the most abundant antibody class in serum, and in humans is present as four subclasses, IgG1- 4, which have distinct properties. IgG binds to antigens via its two Fab regions, and to its effector ligands via its Fc region. IgG is also widely used as a pharmaceutical due to its specific binding to targets. Solution scattering and constrained modelling, along with analytical ultracentrifugation, were used to determine IgG structures in solution. Rabbit IgG was shown to have an asymmetric solution structure, and these structures explained the ability of its two ligands, the Fc receptor and complement C1q, to bind to the top of its Fc region as it is fully accessible and unhindered by the Fab regions. Rabbit IgG also displayed buffer-dependent dimerization. Human IgG4 is distinct from other subclasses as it can undergo Fab-arm exchange and is unreactive compared to the other subclasses. The IgG4 structures were also asymmetric, and blocking of effector binding sites by the Fab regions offered an explanation of the unreactivity of IgG4. Self-association of IgG4 was also observed under certain buffer conditions. In the immune system, human IgG1 is able to bind to all its ligands, and was shown to have an asymmetric solution structure. However, docking studies of the C1q ligand demonstrated that the Fab regions are sufficiently far apart to allow access to effector binding sites. In distinction to rabbit IgG and IgG4, IgG1 did not display significant dimerization under any buffer condition tested. Study of IgG4 under low pH conditions, to mimic chromatography purification steps, revealed that the IgG4 monomer has a more compact structure at pH 3, and gradually forms dimers and higher oligomers. Neutralization of IgG4 to pH 7.4 leads to large amounts of aggregation, with time held at pH 3 and protein concentration important factors in the amount of aggregation observed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available