Abstract
Acidic ostreolysin A/pleurotolysin B (OlyA/PlyB, formerly known as ostreolysin (Oly), and basic 20 kDa equinatoxins (EqTs) are cytolytic proteins isolated from the edible mushroom Pleurotus ostreatus and the sea anemone Actinia equina, respectively. Both toxins, although from different sources, share many similar biological activities: (i) colloid-osmotic shock by forming pores in cellular and artificial membranes enriched in cholesterol and sphingomyelin; (ii) increased vascular endothelial wall permeability in vivo and perivascular oedema; (iii) dose-dependent contraction of coronary vessels; (iv) haemolysis with pronounced hyperkalaemia in vivo; (v) bradycardia, myocardial ischemia and ventricular extrasystoles accompanied by progressive fall of arterial blood pressure and respiratory arrest in rodents. Both types of toxins are haemolytic within nanomolar range concentrations, and it seems that hyperkalaemia plays an important role in toxin cardiotoxicity. However, it was observed that the haemolytically more active EqT III is less toxic than EqT I, the most toxic and least haemolytic EqT. In mice, EqT II is more than 30 times more toxic than OlyA/PlyB when applied intravenously. These observations imply that haemolysis with hyperkalaemia is not the sole cause of the lethal activity of both toxins. Additional mechanisms responsible for lethal action of the two toxins are direct effects on heart, coronary vasoconstriction and related myocardial hypoxia. In this review, we appraise the pathophysiological mechanisms related to the chemical structure of OlyA/PlyB and EqTs, as well as their toxicity.
Highlights
Ostreolysin (Oly) and equinatoxins (EqTs) belong to the group of pore-forming proteins with a defined native conformation which, upon an environmental trigger, is changed spontaneously to enable formation of a transmembrane pore consisting of several protein monomers [1]
Oly was found to consist of two proteins, ostreolysin A (OlyA) and pleurotolysin B (PlyB), produced by the edible mushroom Pleurotus ostreatus in a 9:1 molar ratio, respectively, and with respective ~15 and
The results showed that each subunit of the 13-fold pore of 8 nm in inner diameter comprised a PlyB molecule atop a pleurotolysin A (PlyA) dimer, leading to a respective 2:1 ratio between
Summary
Ostreolysin (Oly) and equinatoxins (EqTs) belong to the group of pore-forming proteins with a defined native conformation which, upon an environmental trigger, is changed spontaneously to enable formation of a transmembrane pore consisting of several protein monomers [1]. ~59 kDa molecular masses [2] Both OlyA/PlyB and EqT II are characterized structurally by a dominant β-structure scaffold that keeps a constant global domain tertiary structure, while the polypeptide elements needed for membrane penetration are provided by minor local conformational changes [3,4]. EqT II recognises the sphingomyelin head group [5], while Oly binds to membrane domains containing both sphingomyelin and cholesterol [2,6]. This binding results in protein oligomerization at the membrane surface, and the formation of transmembrane pores, leading to colloid-osmotic mechanisms resulting in cell lysis. The aim of this review is to summarise the pathophysiological mechanisms related to the chemical structure of both proteins, and to discuss their toxicity on various levels of biological organization
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