Heat denaturation of the antibody, a multi-domain protein

The antibody is one of the most well-studied multi-domain proteins because of its abundance and physiological importance. In this article, we describe the effect of the complex, multi-domain structure of the antibody on its denaturation by heat. Natural antibodies are composed of 6 to 70 immunoglobulin fold domains, and are irreversibly denatured at high temperatures. Although the separated single immunoglobulin fold domain can be refolded after heat denaturation, denaturation of pairs of such domains is irreversible. Each antibody subclass exhibits a distinct heat tolerance, and IgE is especially known to be heat-labile. IgE starts unfolding at a lower temperature compared to other antibodies, because of the low stability of its CH3 domain. Each immunoglobulin domain starts unfolding at different temperatures. For instance, the CH3 domain of IgG unfolds at a higher temperature than its CH2 domain. Thus, the antibody has a mixture of folded and unfolded structures at a certain temperature. Co-existence of these folded and unfolded domains in a single polypeptide chain may increase the tendency to aggregate which causes the inactivation of the antibody.