In situ opening/closing of OmpG from E. coli and the splitting of β-sheet signals in ATR–FTIR spectroscopy

The pH dependent opening and closure of Escherichia coli OmpG is driven by the formation and breaking of hydrogen bridges in β-strands S11–S13. We have investigated the in situ secondary structural changes of OmpG with ATR–FTIR difference spectroscopy in order to detect the signals associated with the newly established interactions. Curve-fitting of OmpG in two pH conditions revealed the splitting and shifting of β-sheet signals upon opening of the channel. Besides secondary structure changes, there are also amino acid side chain signals that play active role in opening/closing of the channel. An interaction among positively charged arginines and negatively charged aspartic and glutamic acid residues is suggested upon closure of the channel while this interaction is abolished when the channel opens at higher pH.

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► β-Sheet signal in IR spectroscopy splits and shifts upon opening of OmpG.
► Opening of OmpG leads to a second β-sheet component in IR spectrum.
► Newly established H-bonds at pH 8 are weaker relative to that of the barrel.
► An interaction among arginines and aspartic/glutamic acid is suggested at pH 5.0.
► Channel gateway is guided by the interaction among positive and negative residues.