Estatin B is a thiol protease inhibitor found by the Thermophilic Bacterium M4323, which is specific to thiol proteases such as papain, fig protease, and bromelain. Estatin B inhibits the production of IgE antibodies but not IgG in mice[1].
References
[1] S Yaginuma, et al. Isolation and characterization of new thiol protease inhibitors estatins A and B. J Antibiot (Tokyo). 1989 Sep;42(9):1362-9. DOI:10.7164/antibiotics.42.1362
