Voltage-dependent Porin-like Ion Channels in the Archaeon Haloferax volcanii

Abstract

Membrane vesicles isolated from the cell envelope of the archaebacterium Haloferax volcanii were either reconstituted in giant liposomes and examined by the patch-clamp technique or were fused into planar lipid bilayers. In addition, cell envelope proteins were solubilized by detergent and reconstituted in azolectin liposomes, which were then fused into planar lipid bilayers. Independently of the technique used the predominant channel activity encountered exhibited the following characteristics. Channels were open at all voltages in the range approximately ؊120 to ؉120 mV and exhibited frequent fast transitions to closed levels of different amplitudes. At voltages greater than 120 mV the channels tended to close in a manner characterized by large, slow transitions of variable amplitudes. The tendency to close at high membrane potentials was much stronger at one polarity. The channel gating pattern was complex exhibiting a range of subconductances of 10 -300 picosiemens in symmetric 100 mM KCl. These electrophysiological characteristics are comparable with those of bacterial and mitochondrial porins, suggesting that the archaeal channels may belong to the general class of porin channels. Some channels showed preference for K ؉ , whereas the others preferred Cl ؊ , suggesting the existence of at least two types of porin-like channels in H. volcanii.

Mechanosensitive Ion Channels of the Archaeon Haloferax volcanii

“…In contrast, the existence of ion channels in cell membranes of Archaea was only recently documented with the discovery of porin-like channels in the archaebacterium Haloferax volcanii (formerly Halobacterium volcanii) (9). In the present study we report the finding of two types of MS ion channels in the plasma membrane of the same microorganism that seem to share many properties of the described bacterial MS 1 ion channels (10 -18).…”

“…Reconstitution of native membrane vesicles yielded several ion channel types, predominantly exhibiting porin-like channel behavior (9). With slight modification of this method of Besnard, Martinac, and Ghazi (9), the presence of porin-like channel activity was minimized.…”

“…Isolation of the Cell Envelope-Cells of H. volcanii were grown and membranes prepared as described previously (9). Cells were cultured in nutrient rich media (in mM: 3350 NaCl, 170 MgCl 2 , 200 MgSO 4 , 6 CaCl 2 , 26 KCl, 6.6 NaHCO 3 , 5.4 NaBr, plus 5 g of yeast extract per liter) until the absorbance A 600 was 1.0, washed three times by centrifugation with phosphate-buffered saline, and the pellet resuspended in 2 mM MgSO 4 , 5% sucrose, 100 mM NaCl, DNase (20 g/ml), 50 mM NaH 2 PO 4 , pH 7.6, and passed twice through a French press at 8,000 psi (Aminco, SLM Instruments, Inc.).…”

Molecular Basis of Bacterial Outer Membrane Permeability Revisited

“…Cell envelopes of Haloferax volcanii were found to contain ion channels that are mostly open, showing a behavior resembling that of porin (55). However, OMs are not known in archaebacteria.…”

The S‐layer protein of Corynebacterium glutamicum is anchored to the cell wall by its C‐terminal hydrophobic domain

“…Some other S-layer proteins show a C-terminal hydrophobic sequence of 20-24 amino acids (the S-layers of Halobacterium halobium (Lechner and Sumper, 1987), Haloferax volcanii (Sumper et al, 1990) and Rickettsia rickettsii (Carl et al, 1990)). In the case of H. volcanii, the presence of porins in the cell wall has been recently demonstrated (Besnard et al, 1996), suggesting the existence of a hydrophobic barrier other than the cytoplasmic membrane in Archaebacteria. Thus, the C-terminal hydrophobic sequence of the S-layer protein of H. volcanii might be anchored in this layer rather than, as has been suggested, in the cytoplasmic membrane.…”