Correlation between the OmpG secondary structure and its pH-dependent alterations monitored by FTIR.
The channel activity of the outer-membrane protein G (OmpG) from Escherichia coli is pH-dependent. To investigate the role of the histidine pair His231/His261 in triggering channel opening and closing, we mutated both histidines to alanines and cysteines. Fourier transform infrared spectra revealed that the OmpG mutants stay-independent of pH-in an open conformation. Temperature ramp experiments indicate that the mutants are as stable as the open state of wild-type OmpG. The X-ray structure of the alanine-substituted OmpG mutant obtained at pH 6.5 confirms the constitutively open conformation. Compared to previous structures of the wild-type protein in the open and closed conformation, the mutant structure shows a difference in the extracellular loop L6 connecting beta-strands S12 and S13. A deletion of amino acids 220-228, which are thought to block the channel at low pH in wild-type OmpG, indicates conformational changes, which might be triggered by His231/His261.
Korkmaz-Ozkan
Filiz
F
Institute of Biophysics, Goethe-University, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main, Germany.
Köster
Stefan
S
Kühlbrandt
Werner
W
Mäntele
Werner
W
Yildiz
Ozkan
O
D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D018360:Crystallography, X-Ray; D003902:Detergents / Q000494:pharmacology; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008055:Lipids / Q000494:pharmacology; D008958:Models, Molecular; D030781:Organisms, Genetically Modified; D018272:Porins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D017510:Protein Folding; D055550:Protein Stability / Q000187:drug effects; D017433:Protein Structure, Secondary / Q000187:drug effects / Q000235:genetics; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
D001425:Bacterial Outer Membrane Proteins; D003902:Detergents; D029968:Escherichia coli Proteins; D007473:Ion Channels; D008055:Lipids; C114347:OmpG protein, E coli; D018272:Porins