title: Differential sensitivity of pneumolysin-induced channels to gating by divalent cations.
abstract: The induction of channels across planar lipid bilayers by purified, recombinant pneumolysin (a hemolytic protein from Streptococcus pneumoniae) has been studied by measuring increases in electrical conductivity. Pneumolysin-induced channels exhibit a wide range of single channel conductances (less than 50 pS to greater than 1 nS at 0.1 M KCl). Channels can be categorized on the basis of their K+:Cl- selectivity: the smallest channels are strongly cation selective, with t+ (the cation transference number) approaching 1.0; the largest channels are unselective (t+ approximately 0.5). Channels tend to remain open at all voltages (-150 to 150 mV); only the smallest channels exhibit any rectification. In the presence of divalent cations (1-5 mM Zn2+; 10-20 mM Ca2+), small (less than 50 pS) and medium-sized (50 pS to 1 nS) channels are closed in a voltage-dependent manner (more closure at higher voltages); at 0 voltage channels reopen. Overall selectivity is reduced by divalent cations, compatible with small, selective channels being closed preferentially to large, nonselective ones. It is concluded that a single molecular species (pneumolysin) induces multiple-sized channels that can be categorized by cation:anion selectivity and by their sensitivity to closure by divalent cations.
authors.affiliation: Department of Cellular & Molecular Sciences, St. George's Hospital Medical School, University of London, United Kingdom.
authors.forename: Y E
authors.initials: YE
authors.lastname: Korchev
authors.forename: C L
authors.initials: CL
authors.lastname: Bashford
authors.forename: C A
authors.initials: CA
authors.lastname: Pasternak
mesh_terms: D001426:Bacterial Proteins; D002118:Calcium / Q000494:pharmacology*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000187:drug effects*; D008051:Lipid Bilayers / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013301:Streptolysins / Q000494:pharmacology*; D015032:Zinc / Q000494:pharmacology*
chemical_list: D001426:Bacterial Proteins; D007473:Ion Channels; D008051:Lipid Bilayers; D013301:Streptolysins; C032290:plY protein, Streptococcus pneumoniae; D015032:Zinc; D002118:Calcium