Small-angle X-ray studies of a human immunoglobulin M

Methacrylate-based short monolithic columns: enabling tools for rapid and efficient analyses of biomolecules and nanoparticles

This review describes the novel chromatography stationary phase--a porous monolithic methacrylate-based polymer--in terms of the design of the columns and some of the features that make these columns attractive for the purification of large biomolecules. We first start with a brief summary of the characteristics of these large molecules (more precisely large proteins like immunoglobulins G and M, plasmid deoxyribonucleic acid (DNA), and viral particles), and a list of some of the problems that were encountered during the development of efficient purification processes. We then briefly describe the structure of the methacrylate-based monolith and emphasize the features which make them more than suitable for dealing with large entities. The highly efficient structure on a small scale can be transferred to a large scale without the need of making column modifications, and the various approaches of how this is accomplished are briefly presented in this paper. This is followed by presenting some of the examples from the bioprocess development schemes, where the implementation of the methacrylate-based monolithic columns has resulted in a very efficient and productive process. Following this, we move back to the analytical scale and demonstrate the efficiency of the monolithic column--where the mass transfer between the stationary and mobile phase is greatly enhanced--for the in-process and final control of the new therapeutics. The combination of an efficient structure and the appropriate hardware results in separations of proteins with residence time less than 0.1 s.

High-molecular-weight protein hydrodynamics studied with a long-lifetime metal-ligand complex

[Ru(2,2'-bipyridine)(2)(4,4'-dicarboxy-2,2'-bipyridine)](2+) (RuBDc) is a very photostable probe that possesses favorable photophysical properties including long lifetime, high quantum yield, large Stokes' shift, and highly polarized emission. In the present study, we demonstrated the usefulness of this probe for monitoring the rotational diffusion of high-molecular-weight (MW) proteins. Using frequency-domain fluorometry with a high-intensity, blue light-emitting diode (LED) as the modulated light source, we compared the intensity and anisotropy decays of RuBDc conjugated to immunoglobulin G (IgG) and immunoglobulin M (IgM), which show a six-fold difference in MW We obtained slightly longer lifetimes for IgM (=428 ns in buffer) than IgG (=422 ns in buffer) in the absence and presence of glycerol, suggesting somewhat more efficient shielding of RuBDc from water in IgM than in IgG. The anisotropy decay data showed longer rotational correlation times for IgM (1623 and 65.7 ns in buffer) as compared to IgG (264 and 42.5 ns in buffer). Importantly, the ratio of the long rotational correlation times of IgM to IgG in buffer was 6.2, which is very close to that of MW of IgM to IgG (6.0). The shorter correlation times are most likely to be associated with domain motions within the proteins. The anisotropy decays reflect both the molecular size and shape of the immunoglobulins, as well as the viscosity. These results show that RuBDc can have numerous applications in studies of high-MW protein hydrodynamics and in fluorescence polarization immunoassays (FPI) of high-MW analytes.

Solution structure of human and mouse immunoglobulin M by synchrotron X-ray scattering and molecular graphics modelling. A possible mechanism for complement activation

The pentameric 71-domain structure of human and mouse immunoglobulin M (IgM) was investigated by synchrotron X-ray solution scattering and molecular graphics modelling. The radii of gyration RG of human IgM Quaife and its Fc5, IgM-S, Fab'2 and Fab fragments were determined as 12.2 nm, 6.1 nm, 6.1 nm, 4.9 nm and 2.9 nm in that order. The RG values were similar for mouse IgM P8 and its Fab'2 and Fab fragments, despite the presence of an additional carbohydrate site. The IgM scattering curves, to a nominal resolution of 5 nm, were compared with molecular graphics models based on published crystallographic alpha-carbon co-ordinates for the Fab and Fc structures of IgG. Good curve fits for Fab were obtained based on the crystal structure of Fab from IgG. A good curve fit was obtained for Fab'2, if the two Fab arms were positioned close together at their contact with the C mu 2 domains. The addition of the Fc fragment close to the C mu 2 domains of this Fab'2 model, to give a planar structure, accounted for the scattering curve of IgM-S. The Fc5 fragment was best modelled by a ring of five Fc monomers, constrained by packing considerations and disulphide bridge formation. A position for the J chain between two C mu 4 domains rather than at the centre of Fc5 was preferred. The intact IgM structure was best modelled using a planar arrangement of these Fab'2 and Fc5 models, with the side-to-side displacement of the Fab'2 arms in the plane of the IgM structure. All these models were consistent with hydrodynamic simulations of sedimentation data. The solution structure of IgM can therefore be reproduced quantitatively in terms of crystallographic structures for the fragments of IgG. Putative Clq binding sites have been identified on the C mu 3 domain. These would become accessible for interaction with Clq when the Fab'2 arms move out of the plane of the Fc5 disc in IgM, that is, a steric mechanism exposing pre-existing Clq sites. Comparison with a solution structure for Clq by neutron scattering shows that two or more of the six globular Clq heads in the hexameric head-and-stalk structure are readily able to make contacts with the putative Clq sites in the C mu 3 domains of free IgM if if the Clq arm-axis angle in solution is reduced from 40 degrees-45 degrees to 28 degrees. This could be the trigger for Cl activation.

CD and small-angle x-ray scattering of silk fibroin in solution

We investigated the structure of silk fibroin dissolved in water and in water-organic solvent mixtures by CD and small-angle x-ray scattering (SAXS). CD spectra indicated a disordered secondary structure in water and a beta-sheet conformation in aqueous organic solvents, such as methanol, dioxane, and trifluoroethanol (in trifluoroethanol a transient form evolving toward beta-sheet conformation was seen just after dissolution). The SAXS technique indicated the presence of fibroin particles of lamellar shape. The molecular weight was 188,000 daltons in water and 302,000 daltons in aqueous methanol.