The staphylococcal alpha-toxin pore has a flexible conformation
The alpha-toxin from Staphylococcus aureus undergoes several conformational changes from the time it is released from the bacterium to the moment it forms a channel in the plasma membrane of its target cell. It is initially a soluble monomer, which undergoes membrane binding and oligomerization into a heptameric ring and finally inserts into the lipid bilayer to form a pore. Here we have analyzed the stability of different forms of the alpha-toxin (monomer as well as heptamers in solution, bound to the membrane and membrane-inserted) by differential scanning calorimetry and limited proteolysis. Data presented here show that, in contrast to both the membrane-bound prepore complex and the monomer in solution, the membrane-inserted alpha-toxin channel does not undergo cooperative unfolding and is highly susceptible to proteases. These observations suggest that the channel has a looser conformation. Interestingly, resistance to proteases could be recovered upon solubilization of the channel, indicating that the loss of rigid tertiary packing only occurred upon membrane insertion. Far-UV CD data, however, suggest that the transmembrane beta-barrel must be stably folded and that therefore only the Cap and Rim domains of the channel are loosely packed. All together, our data show that the alpha-toxin channel is not a rigid complex within the membrane but adopts a rather flexible conformation.
Keywords: Bacterial Toxins/*chemistry/metabolism ; Hemolysin Proteins/*chemistry/metabolism ; Hydrolysis ; Ion Channels/*chemistry ; Liposomes/chemistry ; Models ; Molecular ; Peptide Fragments/chemistry/metabolism ; Phosphatidylcholines/chemistry ; Phosphatidylglycerols/chemistry ; Pronase ; Protein Conformation ; Protein Folding ; Staphylococcus/*chemistry ; Temperature
Microbiology and Tumorbiology Center, Karolinska Institutet, Stockholm, Sweden.
Record created on 2009-01-30, modified on 2016-08-08