title: The solution structures of two human IgG1 antibodies show conformational stability and accommodate their C1q and FcγR ligands.
abstract: The human IgG1 antibody subclass shows distinct properties compared with the IgG2, IgG3, and IgG4 subclasses and is the most exploited subclass in therapeutic antibodies. It is the most abundant subclass, has a half-life as long as that of IgG2 and IgG4, binds the FcγR receptor, and activates complement. There is limited structural information on full-length human IgG1 because of the challenges of crystallization. To rectify this, we have studied the solution structures of two human IgG1 6a and 19a monoclonal antibodies in different buffers at different temperatures. Analytical ultracentrifugation showed that both antibodies were predominantly monomeric, with sedimentation coefficients s20,w (0) of 6.3-6.4 S. Only a minor dimer peak was observed, and the amount was not dependent on buffer conditions. Solution scattering showed that the x-ray radius of gyration Rg increased with salt concentration, whereas the neutron Rg values remained unchanged with temperature. The x-ray and neutron distance distribution curves P(r) revealed two peaks, M1 and M2, whose positions were unchanged in different buffers to indicate conformational stability. Constrained atomistic scattering modeling revealed predominantly asymmetric solution structures for both antibodies with extended hinge structures. Both structures were similar to the only known crystal structure of full-length human IgG1. The Fab conformations in both structures were suitably positioned to permit the Fc region to bind readily to its FcγR and C1q ligands without steric clashes, unlike human IgG4. Our molecular models for human IgG1 explain its immune activities, and we discuss its stability and function for therapeutic applications.
authors: From the Department of Structural and Molecular Biology, Division of Biosciences, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors: Lucy E
authors: LE
authors: Rayner
authors: From the Department of Structural and Molecular Biology, Division of Biosciences, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors: Gar Kay
authors: GK
authors: Hui
authors: From the Department of Structural and Molecular Biology, Division of Biosciences, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors: Jayesh
authors: J
authors: Gor
authors: the ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, United Kingdom, and.
authors: Richard K
authors: RK
authors: Heenan
authors: the Department of Biochemical Engineering, Division of Engineering, Roberts Building, University College London, Gower Street, London WC1E 7JE, United Kingdom.
authors: Paul A
authors: PA
authors: Dalby
authors: From the Department of Structural and Molecular Biology, Division of Biosciences, Darwin Building, University College London, Gower Street, London WC1E 6BT, United Kingdom, s.perkins@ucl.ac.uk.
authors: Stephen J
authors: SJ
authors: Perkins
mesh_terms: D015922:Complement C1q / Q000737:chemistry*; D006801:Humans; D007074:Immunoglobulin G / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D033363:Neutron Diffraction; D011485:Protein Binding; D055550:Protein Stability; D017452:Receptors, IgG / Q000737:chemistry*; D012996:Solutions; D014961:X-Ray Diffraction
chemical_list: D007074:Immunoglobulin G; D008024:Ligands; D017452:Receptors, IgG; D012996:Solutions; D015922:Complement C1q
keywords: Analytical Ultracentrifugation; Antibody; Molecular Modeling; Neutron Scattering; X-ray Scattering