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.
Vécsey-Semjén
B
B
Microbiology and Tumorbiology Center, Karolinska Institutet, Stockholm, Sweden.
Knapp
S
S
Möllby
R
R
van der Goot
F G
FG
D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000378:metabolism; D006868:Hydrolysis; D007473:Ion Channels / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D011402:Pronase; D011487:Protein Conformation; D017510:Protein Folding; D013210:Staphylococcus / Q000737:chemistry*; D013696:Temperature
D001427:Bacterial Toxins; D006460:Hemolysin Proteins; D007473:Ion Channels; D008081:Liposomes; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; C021091:staphylococcal alpha-toxin; C051388:1,2-dioleoyl-sn-glycero-3-phosphoglycerol; D011402:Pronase; C017251:1,2-oleoylphosphatidylcholine