Structure and function of pneumolysin, the multifunctional, thiol-activated toxin of Streptococcus pneumoniae.

Pneumolysin is a thiol-activated, membrane-damaging, multifunctional toxin and a known virulence factor of Streptococcus pneumoniae. The toxin can interfere with the functioning of both cellular and soluble components of the human immune system which protects against pneumococcal infection. Different amino acids within the toxin which are important in promoting oligomerization of the toxin in membranes and for the generation of functional lesions have been identified by site-directed mutagenesis. Pneumolysin can also activate the classical pathway of complement, and this appears to involve antibody binding (via Fc) by a region of the toxin homologous to C-reactive protein, a human acute-phase protein also capable of classical pathway activation and implicated in host defence against pneumococcal infection.