Stabilization of dissociable IgA2 proteins by secretory component
Jerry, L.M.; Kunkel, H.G.; Adams, L.
Journal of Immunology 109(2): 275-283
1972
ISSN/ISBN: 0022-1767 PMID: 4625844 Document Number: 50978
The Am2(+) genetic variant of human IgA2 immunoglobulins is potentially unstable because it lacks disulphide bridges between the heavy (H) and light (L) chains. It dissociates spontaneously under denaturing conditions into heavy and light chain dimer subunits (H2, L2), without the need for prior reduction. Isolated secretory component (SC) and bovine SC will bind to and stabilize the polymer forms of these myeloma proteins, but only human SC will bind to and stabilize monomeric proteins. The reaction involves the whole IgA2 molecule rather than just its subunits. Moreover, SC will stabilize a pepsin F(ab')2 fragment. Since stabilization is prevented by iodoacetic acid, covalent disulphide bonding appears to be involved. The ability of SC to stabilize the potentially dissociable AM2(+) genetic variant of IgA2 may enhance its capacity to function in external secretions.