Conformation of human IgG subclasses in solution

Abstract

The structure of six human myeloma proteins: IgGl(Bal), IgG2(Klu), IgG3(Bak), IgG3(Het), IgG4(Kov) and IgG4(Pol), was studied in solution using small-angle X-ray scattering and hydrodynamic methods. For IgGl (Bal) and IgG3(Het) the experimental data, including radius of gyration (R",), radii of gyration of the cross-section (Rql, RqJ, intrinsic viscosity [q], sedimentation coefficient SO^^,^) and molecular mass, were interpreted in terms of structural models based on the Fab and Fc conformations, observed in crystal, by varying the relative positions of the Fab and Fc parts, i.e. their relative angles and distances. IgGl(Ba1) can be resolved by proposing a 'non-planar' (tetrahedral) molecular shape, in which the long hinge peptide is in a folded conformation and the two Fab and Fc parts are in a closely packed arrangement. In this model the angle between the two Fab arms is about 90", in the average position.The X-ray scattering and hydrodynamic behaviour of the IgG2 and IgG4 types of antibodies appeared to be similar to IgGl(Ba1). The parameters of the two IgG3 proteins are similar while they are different to the others.Immunoglobulins are closely related proteins having a common fundamental structure. Based on differences in the constant part of the molecules, human immunoglobulins are classified into five classes. The most abundant human immunoglobulin class, IgG, is a mixture of four subclasses with differing structure and antigenic types of the heavy chains [I -31. The functional significance of the existence of the four IgG subclasses is not completely clear, although subclassrelated differences in complement fixation [4] [8, 18, 271. The proposed structures indicate the dominating differences in the y chains which are localized in the hinge region [29]. It is known that the structure of the hinge region can influence the segmental flexibility within the IgG molecules and it plays a role in their overall structure [I 1, 12,301. However, our knowledge about the conformation and the functional role of the hinge region is far from complete. Substantial differences have been described in the primary structure of the hinge [29] among human IgG subclasses; therefore, these proteins offer a good system for comparative studies to answer the question of whether the differences in the hinge sequence are reflected in the overall conformation of IgG. Since IgG molecules function as intact, dissolved particles, our aim was to conduct solution studies on complete IgGs. Myeloma proteins are homogeneous monoclonal populations representing a single subclass and, therefore, provide suitable systems for such physico-chemical studies. Smallangle X-ray scattering and hydrodynamic methods were chosen as the best applicable methods to provide information about the overall shape of macromolecules in solution.Particular care was taken to avoid aggregate formation in the X-ray scattering measurements. Our attention was focussed on the structural differences between the most abundant'IgG1 and the controversial IgG3 subclasses....

The Solution Structures of Two Human IgG1 Antibodies Show Conformational Stability and Accommodate Their C1q and FcγR Ligands

“…The use of three NaCl concentrations examined potential electrostatic effects on the IgG1 structure, whereas heavy water is a known promoter of protein self-association. By comparison, earlier scattering studies on human IgG1 reported few scattering and ultracentrifugation runs or were performed in nonphysiological buffer conditions (28,38,39,(47)(48)(49). Both IgG1 6a and IgG1 19a showed similar experimental R g and R xs values and the same overall length of 16 nm ( Table 1 6.3-6.4 S, which were indistinguishable within error.…”

“…4). A major monomer peak was observed at s 20 (38,39,40). Both IgG1 6a and IgG1 19a were predominantly monomeric in solution and were accompanied by a minor dimer peak.…”

Binding of plasma proteins to titanium dioxide nanotubes with different diameters

“…79 Even though IgG possess a unique quaternary structure, 87 the binding ratio on NTs remained comparable with other studied proteins. With denaturated IgG, however, the three dimensional conformation was destroyed and, consequentially, the binding was reduced, with the trend of binding with regard to the NTs diameters remaining unchanged.…”

Hydrodynamic study of flexibility in immunoglobulin igG1 using Brownian dynamics and the Monte Carlo simulations of a simple model

“…In Table I1 these results are shown along with the experimental ones. 12 We can see that differences between both theoretical treatments are negligible in the rigid limit. Differences in the flexible limit are due to the small but finite probability of overlapping between beads that is allowed by the Lennard-Jones potential and that is not considered in the rigidbody approximation.…”