Modulation of the SecY channel permeability by pore mutations and trivalent cations

The SecY channel serves to transport proteins across the bacterial inner membrane. The closed channel is impermeable to small molecules by means of a plug domain and a hydrophobic pore, consisting of six conserved isoleucine residues. The substitution of these isoleucines by asparagine leads to the selective conductance of small monovalent anions, especially chloride. In this addendum, we show that replacement of the isoleucine residues by bulky phenylalanine also leads to an increased chloride conductance, suggesting that hydrophobicity of the pore is not the sole determinant for maintaining channel impermeability. Instead, incubation of the membrane with the trivalent cation Al(3+) dramatically increases Cl(-) transport across the wild type SecY channel, suggesting that surface charge density around the SecY pore plays a significant role during the process of chloride conductance.