Isolation, Characterization, and Biocompatibility of Bisporitin, a Ribotoxin-like Protein from White Button Mushroom ( Agaricus bisporus )

White button mushroom ( (J.E. Lange) Imbach) is one of the widely consumed edible mushrooms. Indeed, fruiting bodies are a rich source of nutrients and bioactive molecules. In addition, several enzymes with biotechnological applications are found in (e.g., enzymes for lignocellulose degradation). Here, a novel ribotoxin-like protein (RL-P) from the edible mushroom was purified and characterized. This RL-P, named bisporitin, is a monomeric protein (17-kDa) exhibiting specific ribonucleolytic activity by releasing the α-fragment (hallmark of RL-Ps) when incubated with rabbit ribosomes. In addition, bisporitin shows magnesium-dependent endonuclease activity and displays a similar far-UV CD spectrum as ageritin, the prototype of RL-Ps, isolated from fruiting bodies. Interestingly, bisporitin is the first member of RL-Ps to have noticeably lower thermal stability (T = 48.59 ± 0.98 °C) compared to RL-Ps isolated in other mushrooms (T > 70 °C). Finally, this protein is only partially hydrolyzed in an in vitro digestive system and does not produce adverse growing effects on eukaryotic cell lines. This evidence paves the way for future investigations on possible bioactivities of this RL-P in the digestive system.