ISSN:
1432-1424
Keywords:
pneumolysin
;
ion channels
;
lipid bilayers
;
gating
;
divalent cations
;
toxin
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary 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 (〈50 pS to 〉1 nS at 0.1 m KCl). Channels can be categorized on the basis of their K+:C− selectivity: the smallest channels are strongly cation selective, with t+ (the cation transference number) approaching 1.0; the largest channels are unselective (t+ ≈ 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 (〈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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00231507
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