Abstract
The cholesterol-dependent cytolysins (CDCs) constitute a family of pore-forming toxins that contribute to the pathogenesis of a large number of Gram-positive bacterial pathogens.The most highly conserved region in the primary structure of the CDCs is the signature undecapeptide sequence (ECTGLAWEWWR). The CDC pore forming mechanism is highly sensitive to changes in its structure, yet its contribution to the molecular mechanism of the CDCs has remained enigmatic. Using a combination of fluorescence spectroscopic methods we provide evidence that shows the undecapeptide motif of the archetype CDC, perfringolysin O (PFO), is a key structural element in the allosteric coupling of the cholesterol-mediated membrane binding in domain 4 (D4) to distal structural changes in domain 3 (D3) that are required for the formation of the oligomeric pore complex. Loss of the undecapeptide function prevents all measurable D3 structural transitions, the intermolecular interaction of membrane bound monomers and the assembly of the oligomeric pore complex. We further show that this pathway does not exist in intermedilysin (ILY), a CDC that exhibits a divergent undecapeptide and that has evolved to use human CD59 rather than cholesterol as its receptor. These studies show for the first time that the undecapeptide of the cholesterol-binding CDCs forms a critical element of the allosteric pathway that controls the assembly of the pore complex.
Highlights
The cholesterol-dependent-cytolysin (CDC) family of toxins consists of over 25 members that are produced by many different species of Gram-positive bacterial pathogens [1] and contribute in various ways to the pathogenesis of these organisms [2,3,4,5]
The cholesterol-dependent cytolysins (CDCs) are a large family of pathogenesis-associated pore-forming toxins that are expressed by many Grampositive pathogens
The studies show that the undecapeptide forms a critical structural element in the allosteric pathway that couples membrane binding to cholesterol to the initiation of distal structural changes, which are required for the assembly of the pore forming complex
Summary
The cholesterol-dependent-cytolysin (CDC) family of toxins consists of over 25 members that are produced by many different species of Gram-positive bacterial pathogens [1] and contribute in various ways to the pathogenesis of these organisms [2,3,4,5]. Members of this family exhibit high levels of homology in their primary structures (40–70%) and in the crystal structures of their soluble monomers [6,7,8,9]. These studies suggest that the undecapeptide plays an important role in the CDC poreforming mechanism, yet since Iwamoto et al [16] began studying the effects of chemically altering the undecapeptide in 1987 its contribution to the pore forming mechanism of the CDCs has remained elusive
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