A new toxic protein from death cap Amanita phalloides: isolation and study of cytotoxic activity

Abstract

Cytotoxic protein from fruit body of the death cap Amanita phalloides mushroom, designated as toxophallin, has been isolated and its principal physico-chemical and biological properties have been characterized. This protein possesses molecular mass 55 kDa and isoelectric point at pH 5.7 and is expressed predominantly in the stem of mushroom fruit body. As assessed by cross-linking experiments, toxophallin forms a trimeric complex in buffered solution. It induces apoptosis in several mammalian cells lines (murine L1210 and CCL-64, and human A549) with IC50 at 0.25–0.45 ug/ml. It also induces DNA fragmentation and morphological changes in the nuclei of target cells (chromatin condensation and fragmentation of nuclei) that are characteristic for apoptosis. Caspase III Inhibitor (Boc-D-fmk) does not inhibit toxophallin-induced apoptotic DNA fragmentation, suggesting that this toxin involves caspase-independent pathway of apoptosis. Besides, it was shown that toxophallin interaction with target cells is not mediated by specific cell surface receptor. Thus, toxophallin is a new toxic protein whose properties distinguish it from other toxic compounds (cyclopeptides and phallolysin) earlier found in the death cap.

Keywords

• toxic protein
• death cap amanita phalloides
• apoptosis