Two structural transitions in membrane pore formation by pneumolysin, the pore-forming toxin of Streptococcus pneumoniae

A study was conducted to determine the structure of soluble pneumolysin monomers that are produced by the human pathogen Streptococcus pneumoniae. Using cryo-electron microscopy, the three-dimensional structure of a helical oligomer of pneumolysin and of a membrane-bound ring form was revealed. The diameter of the helical form was estimated to be at 41 subunits per turn while a number of subunits per ring was observed to be in the range of 40-50.