Crystallohydrodynamics for solving the hydration problem for multi-domain proteins: open physiological conformations for human IgG

• Published in: Biophysical chemistry Vol. 93; no. 2; pp. 181 - 196
• Main Authors: Carrasco, Beatriz, Garcia de la Torre, Jose, Davis, Kenneth G, Jones, Susan, Athwal, Diljeet, Walters, Chris, Burton, Dennis R, Harding, Stephen E
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 28-11-2001
• Subjects: Crystallography, X-Ray; Crystallohydrodynamics; Human IgG; Humans; Hydration; Immunoglobulin G - chemistry; Models, Molecular; Protein Conformation; Proteins; Ultracentrifugation; Water - chemistry; Proteins; Crystallohydrodynamics; Hydration; Human IgG
• ISSN: 0301-4622; 1873-4200
• DOI: 10.1016/S0301-4622(01)00220-4

Hydrodynamic methods provide a route for studying the low-resolution conformation — in terms of time-averaged spatial orientation of the Fab′ and Fc domains relative to each other — of the human IgG subclasses, IgG1, IgG2, IgG3 and IgG4 in the environment in which many exist naturally — a solution. Representative modelling strategies are now available using ‘shell-bead’ or ‘shell’ modelling of the surface of the molecules with the size-independent programme
solpro [J. Garcia de la Torre, S.E. Harding, B. Carrasco, Eur. Biophys. J. 28 (1999) 119–132]. The shell model fits to the equivalent inertial surface ellipsoids of the published crystal structures for the Fab′ and Fc domains of IgG are made and an apparent hydration δ
app of 0.51g/g for Fab′ and 0.70 g/g for the glycoprotein Fc are obtained, which yield an average value of (0.59±0.07) g/g for the intact antibody (2 Fab′+1 Fc). The relative orientations of these domains for each of the IgG subclasses is then found (using where appropriate a cylindrical hinge) from
solpro by modelling the Perrin function,
P (i.e. ‘frictional ratio due to shape’) using this δ
app and experimentally measured sedimentation coefficients. All the IgG subclasses appear as open, rather than compact structures with the degree of openness IgG3>IgG1>(IgG2, IgG4), with IgG3 and IgG1 non-coplanar. The hingeless mutant IgGMcg, with
s°
20,w∼6.8 S yields a coplanar structure rather similar to IgG2 and IgG4 and consistent with its crystallographic structure. The extension of this procedure for representing solution conformations of other antibody classes and other multi-domain proteins is indicated.