The solution structures of native and patient monomeric human IgA1 reveal asymmetric extended structures: implications for function and IgAN disease.
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.
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, U.K.
Gar Kay
GK
Hui
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, U.K.
David W
DW
Wright
Department of Infection, Immunity and Inflammation, Maurice Shock Medical Sciences Building, University of Leicester, University Road, Leicester LE1 9HN, U.K.
Owen L
OL
Vennard
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, U.K.
Lucy E
LE
Rayner
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, U.K.
Melisa
M
Pang
Department of Infection, Immunity and Inflammation, Maurice Shock Medical Sciences Building, University of Leicester, University Road, Leicester LE1 9HN, U.K.
See Cheng
SC
Yeo
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, U.K.
Jayesh
J
Gor
Department of Infection, Immunity and Inflammation, Maurice Shock Medical Sciences Building, University of Leicester, University Road, Leicester LE1 9HN, U.K.
Karen
K
Molyneux
Department of Infection, Immunity and Inflammation, Maurice Shock Medical Sciences Building, University of Leicester, University Road, Leicester LE1 9HN, U.K.
Jonathan
J
Barratt
Department of Structural and Molecular Biology, Darwin Building, University College London, Gower Street, London WC1E 6BT, U.K. s.perkins@ucl.ac.uk.
Stephen J
SJ
Perkins
D018360:Crystallography, X-Ray; D005260:Female; D005922:Glomerulonephritis, IGA; D006801:Humans; D007070:Immunoglobulin A / Q000737:chemistry* / Q000378:metabolism; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry* / Q000378:metabolism; D007141:Immunoglobulin Fc Fragments / Q000737:chemistry* / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D066263:Protein Aggregation, Pathological; D020836:Protein Structure, Quaternary
D007070:Immunoglobulin A; D007140:Immunoglobulin Fab Fragments; D007141:Immunoglobulin Fc Fragments
X-ray scattering; analytical ultracentrifugation; antibody; constrained modelling; human immunoglobulin A1 (IgA1); immunoglobulin A (IgA) nephropathy; neutron scattering