The solution structures of native and patient monomeric human IgA1 reveal asymmetric extended structures: implications for function and IgAN disease.
journal contributionposted on 18.02.2016, 11:13 by G. K. Hui, D. W. Wright, Owen L. Vennard, L. E. Rayner, M. Pang, See Cheng Yeo, J. Gor, Karen Molyneux, Jonathan Barratt, S. J. Perkins
Native IgA1, for which no crystal structure is known, contains an O-galactosylated 23-residue hinge region that joins its Fab and Fc regions. IgA nephropathy (IgAN) is a leading cause of chronic kidney disease in developed countries. Because IgA1 in IgAN often has a poorly O-galactosylated hinge region, the solution structures of monomeric IgA1 from a healthy subject and three IgAN patients with four different O-galactosylation levels were studied. Analytical ultracentrifugation showed that all four IgA1 samples were monomeric with similar sedimentation coefficients, s(0)20,w. X-ray scattering showed that the radius of gyration (Rg) slightly increased with IgA1 concentration, indicating self-association, although their distance distribution curves, P(r), were unchanged with concentration. Neutron scattering indicated similar Rg values and P(r) curves, although IgA1 showed a propensity to aggregate in heavy water buffer. A new atomistic modelling procedure based on comparisons with 177000 conformationally-randomized IgA1 structures with the individual experimental scattering curves revealed similar extended Y-shaped solution structures for all four differentially-glycosylated IgA1 molecules. The final models indicated that the N-glycans at Asn(263) were folded back against the Fc surface, the C-terminal tailpiece conformations were undefined and hinge O-galactosylation had little effect on the solution structure. The solution structures for full-length IgA1 showed extended hinges and the Fab and Fc regions were positioned asymmetrically to provide ample space for the functionally-important binding of two FcαR receptors to its Fc region. Whereas no link between O-galactosylation and the IgA1 solution structure was detected, an increase in IgA1 aggregation with reduced O-galactosylation may relate to IgAN.
CitationBiochem J, 2015, 471 (2), pp. 167-185
Author affiliation/Organisation/COLLEGE OF MEDICINE, BIOLOGICAL SCIENCES AND PSYCHOLOGY/School of Medicine/Department of Infection, Immunity and Inflammation
VersionVoR (Version of Record)
Published inBiochem J
PublisherPortland Press for Biochemical Society
X-ray scatteringanalytical ultracentrifugationantibodyconstrained modellinghuman immunoglobulin A1 (IgA1)immunoglobulin A (IgA) nephropathyneutron scatteringCrystallography, X-RayFemaleGlomerulonephritis, IGAHumansImmunoglobulin AImmunoglobulin Fab FragmentsImmunoglobulin Fc FragmentsMaleModels, MolecularProtein Aggregation, PathologicalProtein Structure, Quaternary