Labile Disulfide Bonds and Free Thiol Groups in Human IgG I.

Abstract

The content of free SH groups (about 0.24) and labile S-S bonds (about 0.64) per mole human IgG can be differentially determined by the reaction with 5,5′-dithio(2,2′-dinitro)benzoate (DTNB) for 30 min and 24 h, respectively. Highly significant linear correlations were found between the number of labile S-S and the percentage of IgG₁, and the number of free SH and the percentage of IgG₂ of the total IgG fraction. It is concluded that the IgG₁ molecule contains one S-S bond which is opened during the 24 h interaction with DTNB by a disulfide exchange reaction. This was also confirmed by the investigation of pure monomeric IgG₁. The splitting of this bond does not alter molecular weight, antigenic properties or antigen binding activity, but reduces significantly the complement binding activity of IgG. On the other hand, one free SH group could be found in the IgG₂ molecule. Changes have been observed in SH and S-S levels of total IgG in patients with various malignant diseases that are to be explained by corresponding changes of the percentages of IgG₁ and IgG₂.

Modulation of the Effector Functions of a Human IgG1 through Engineering of Its Hinge Region

“…Conversely, increasing the flexibility of the middle hinge negatively affects binding to C1q (variants 3, 4, 5, and 6). The important role played by each of the two middle hinge covalent bonds (variant 5 and 6) is in agreement with previous results suggesting that the opening of the bridge formed by the middle hinge upper cysteine results in a dramatic loss of complement binding (37,38). Thus, we show here that the role played by the middle hinge lower cysteine is also a determinant one.…”

Disulfide bond structures of IgG molecules

“…However, free sulfhydryls has been routinely detected in IgG molecules, including IgG from serum and recombinant mAbs ( Table 1). [28][29][30][31][32][33][34][35] It is worthwhile to discuss two important observations in Table 1. First, higher level of free sulfhydryls was detected under denaturing conditions compared with native conwhile the two major non-classical structures were referred to as IgG 2 B and IgG 2 -A/B, the latter being considered a structural intermediate between IgG 2 A and IgG 2 B (Fig.…”

Reactive disulfide bonds in immunoglobulin G. A unique feature in serum proteins of different species

“…This indicated an additional binding of 35S-NBSSBN (or its half molecules) to proteins belonging to this serum component. As immunoglobulins G, making up to 70-75% of '/-globulins, had been presumably involved, monomeric IgG was isolated in Tris-HCl-buffer pH 7.2 from serum [7,8] and mixed with a solution of unlabelled NBSSBN. After 30 minutes, a yellow eolour appeared with absorption maximum at 410 nm.…”