Constant region of immunoglobulin heavy chains. Immunoglobulins, also known as antibodies, are membrane-bound or secreted glycoproteins produced by B lymphocytes. In the recognition phase of humoral immunity, the membrane-bound immunoglobulins serve as receptors which, upon binding of a specific antigen, trigger the clonal expansion and differentiation of B lymphocytes into immunoglobulins-secreting plasma cells. Secreted immunoglobulins mediate the effector phase of humoral immunity, which results in the elimination of bound antigens. The antigen binding site is formed by the variable domain of one heavy chain, together with that of its associated light chain. Thus, each immunoglobulin has two antigen binding sites with remarkable affinity for a particular antigen. The variable domains are assembled by a process called V-(D)-J rearrangement and can then be subjected to somatic hypermutations which, after exposure to antigen and selection, allow affinity maturation for a particular antigen. Ig alpha is the major immunoglobulin class in body secretions.
Background References
1. Fahrbach KM et al. Differential binding of IgG and IgA to mucus of the female reproductive tract. PLoS One 8:e76176 (2013).
2. Kang S et al. In situ identification and localization of IGHA2 in the breast tumor microenvironment by mass spectrometry. J. Proteome Res. 11:4567-4574 (2012).
Post-translational Modification
3-Hydroxykynurenine, an oxidized tryptophan metabolite that is common in biological fluids, reacts with alpha-1-microglobulin to form heterogeneous polycyclic chromophores including hydroxanthommatin. The chromophore reacts with accessible cysteines forming non-reducible thioether cross-links with Ig alpha-1 chain C region Cys-352.; N- and O-glycosylated. N-glycan at Asn-144: Hex5HexNAc4.
Western blot analysis of IgA on human plasma lysate. Proteins were transferred to a PVDF membrane and blocked with 5% BSA in PBS for 1 hour at room temperature. The primary antibody was used at a 1/500 dilution in 5% BSA at room temperature for 2 hours. Goat Anti-Mouse IgG - HRP Secondary Antibody (HA1006) at 1:5,000 dilution was used for 1 hour at room temperature.
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