The SecY complex forms a channel capable of ionic discrimination.
Protein translocation across the bacterial membrane occurs at the SecY complex or channel. The resting SecY channel is impermeable to small molecules owing to a plug domain that creates a seal. Here, we report that a channel loosely sealed, or with a plug locked open, does not, however, lead to general membrane permeability. Instead, strong selectivity towards small monovalent anions, especially chloride, is observed. Mutations in the pore ring-structure increase both the translocation activity of the channel and its ionic conductance, however the selectivity is maintained. The same ionic specificity also occurs at the onset of protein translocation and across the archaeal SecY complex. Thus, the ion-conducting characteristic of the channel seems to be conserved as a normal consequence of protein translocation. We propose that the pore ring-structure forms a selectivity filter, allowing cells to tolerate channels with imperfect plugs.
Dalal
Kush
K
Department of Biochemistry and Molecular Biology, Life Sciences Institute, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia, Canada.
Duong
Franck
F
D000596:Amino Acids / Q000378:metabolism; D004553:Electric Conductivity; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000378:metabolism*; D007477:Ions; D050505:Mutant Proteins / Q000378:metabolism; D010539:Permeability; D021381:Protein Transport; D011522:Protons; D000069816:SEC Translocation Channels
D000596:Amino Acids; D029968:Escherichia coli Proteins; D007473:Ion Channels; D007477:Ions; D050505:Mutant Proteins; D011522:Protons; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli