Tryptic peptides of human thyroglobulin: I. Immunoreactivity with murine monoclonal antibodies

Human thyroglobulin (Tg) was treated with trypsin at different concentrations of trypsin/Tg for various incubation times at 37°C using non-reducing conditions. A ratio of trypsin to Tg of 1:100 (w/w) was optimal to release small peptides that were reactive to murine MoAbs to human Tg. Most peptides were released after only 1 h incubation with trypsin, but these peptides were further degraded at longer incubation times. However, a few small peptides, the largest of which with an apparent molecular weight (MW(ap)) of 40 kD, resisted tryptic digestion up to at least 12 h of incubation. These resistant peptides were further degraded by trypsin at 18-24 h of incubation. Tryptic peptides of Tg, released at 1 h and 4 h of incubation, were analysed for their immunoreactivity to 16 well terized anti-Tg MoAbs by Western immunoblot. Patterns of peptide recognition of these MoAbs were generally unique. Eight MoAbs reacted with peptides of MW(ap) of 10-25 kD and above. Four other MoAbs reacted with peptides of MW(ap) of 25-43 kD and above, and the remaining four reacted with peptides of MW(ap) > 43 kD. Nine of these MoAbs failed to recognize peptides after reduction, suggesting that the MoAbs bind conformation-dependent epitopes. The above information will promote the development of models relating the structure of Tg to the autoimmune process, and may provide an understanding of those regions of Tg responsible for the induction of autoimmune thyroiditis.