Human myeloma IgG4 reveals relatively rigid asymmetric Y-like structure with different conformational stability of C2 domains.

Human IgG4 (hIgG4) has weak pro-inflammatory activity. The structural basis for this is still unclear. Here a 3D model of myeloma hIgG4 was created at ∼3nm resolution using electron microscopy (EM) with negative staining and single-particle 3D reconstruction.

Large is fast, small is tight: determinants of speed and affinity in subunit capture by a periplasmic chaperone.

The chaperone/usher pathway assembles surface virulence organelles of Gram-negative bacteria, consisting of fibers of linearly polymerized protein subunits. Fiber subunits are connected through 'donor strand complementation': each subunit completes the immunoglobulin (Ig)-like fold of the neighboring subunit by donating the seventh β-strand in trans. Whereas the folding of Ig domains is a fast first-order process, folding of Ig modules into the fiber conformation is a slow second-order process.

Resolving the energy paradox of chaperone/usher-mediated fibre assembly.

Periplasmic chaperone/usher machineries are used for assembly of filamentous adhesion organelles of Gram-negative pathogens in a process that has been suggested to be driven by folding energy. Structures of mutant chaperone-subunit complexes revealed a final folding transition (condensation of the subunit hydrophobic core) on the release of organelle subunit from the chaperone-subunit pre-assembly complex and incorporation into the final fibre structure. However, in view of the large interface between chaperone and subunit in the pre-assembly complex and the reported stability of this complex, it is difficult to understand how final folding could release sufficient energy to drive assembly.

Folding of the human immunoglobulin G3 Kus core hinge into the thirteenth globular domain.

Earlier, the electron microscopy and hydrodynamic studies revealed the transformation of the globule-like form of the human (h) IgG3 Kus hinge into a rod-like shape under non-denaturing perturbations [Eur. J. Biochem.

Core hinge of human immunoglobulin G3 as a system of four independent co-operative blocks.

On the heat absorption curves of human immunoglobulin G3 (hIgG3) Kuc melting the scanning calorimetry method reveals a high-temperature (high-T(m)) peak of high intensity that is absent at the curves of other hIgG subclasses and IgG of other species. An analogous peak is observed also at the curves of melting of hIgG3 fragments containing the hinge segments. The high-T(m) peak is accompanied by characteristic changes in circular dichroism (CD) spectra at 220-230 nm.

Long-term metastable conformation of human Fcgamma subunit.

It was found that the human (hu) myeloma IgG1 Ser, its Fcgamma fragment and the chimeric mouse-human monoclonal antibody (chim-mAb), containing the constant part of hu-gamma1-chain, can exist in a long-term metastable conformational state. This state arises as a result of short incubation of IgG molecules and their Fcgamma fragments at pH<2.8 and the consequent rapid neutralisation to pH 7.