Structural studies of immunoglobulins spin-labeled at the carbohydrate moiety

Interactions between immunoglobulin G molecules

“…After periodate oxidation the oligosaccharide chain can be labeled by spin labels with a free amino group [30]. The influence of IC formation on the mobility of the spin label linked to Fc oligosaccharide was studied using murine anti-DNP antibodies of the IgG2a subclass [31].…”

Spin-labeled carbohydrates

“…Thus, aldehydo or keto sugars were converted to aldo nitrones or keto nitrones A by previously described methods.40,41 These starting materials underwent nucleophilic additions with either Grignard reagents or cyanide ion to give the corresponding desoxyhydroxylamino sugars B. The latter, in turn, were oxidized (air, periodic acid, lead dioxide) to the sugar nitroxyls C. were oxidized to the corresponding nitroxyl derivatives [95][96][97][98][99][100][101][102][103] (Scheme XXI). The reactions leading to the (3 series (85)(86)(87)(88)(89)(90)(91)(92)(93)(94) were reported to be generally stereoselective and sometimes stereospecific.39 Solutions of these intermediates oxidize in air to the nitroxyl C series, however better yields were obtained with either periodic acid or lead dioxide.…”

“…The ESR spectra of immunoglobulins belonging to different classes and labeled with the same spin label do not differ significantly. 103 The spin label to protein molar ratios for various immunoglobulins that were spin labeled on the carbohydrate groups are as follows: IgG, 1.0-1.8; IgE, 8; IgM, 30.103 There is a higher carbohydrate content in IgE and IgM than in IgG.…”

“…118 Labeling the Fc regions of IgM, its 7S subunit (IgM7S), and (Fc)5 fragments yielded nearly identical rc values, ranging from 6.5 to 7.5 ns. 103 The ESR spectrum consisted of two components as a result of increasing the viscosity at constant temperature. This result could be attributed to the binding of nitroxyl 5 to two types of carbohydrate chains in IgM, one more mobile the other less mobile.…”

“…128 It was shown that binding of the hapten occurred in the Fab region of these antibodies.128 These two results when combined support the concept that hapten binding at the Fab region causes a conformational change which is transmitted through the macromolecule to the Fc region, causing a change in rotational mobility of the nitroxyl spin label. 103,107 Mention was made of a study of a complex formation between a spin-labeled polysaccharide antigen from pneumococcus SII and an excess of rabbit antihuman IgG antibody.103 There was a change in the ESR spectrum characteristic of a reduced mobility of bound spin label. This change in mobility probably occurred because of an immobilization of a part of this large antigen in the antigen combining site.…”