Increasing Chloride Conductance Through the SecY Complex By Mutagenesis or Trivalent Cations

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The SecY complex or channel is responsible for translocation of proteins across the bacterial inner membrane. The complex maintains a seal for small molecules by means of a plug domain and a hydrophobic pore, consisting of six isoleucine residues arranged in a ring. When these pore residues are mutated into asparagine, a specific conductance for small monovalent anions, like chloride, is observed. Here, we show that an enhanced chloride conductance is also observed when bulky phenylalanine residues are introduced into the pore ring. The increased conductance is accompanied by an increase in protein translocation. Chloride conductance was also observed upon addition of trivalent aluminum cations, which are suspected of binding to negatively charged residues near the lateral gate of SecY.