Calcium ion-mediated opening of the channel gate in the Pseudomonas aeruginosa porin.
The gate-forming domain of protein D2 (OprD2) in the outer membrane of Pseudomonas aeruginosa contains an amino acid sequence homologous to the calcium-binding site of the myosin light chain. This observation lets us to test the effect of Ca2+ on the channel function of OprD2. The diffusion rate of p-nitrophenyl phosphate (PNPP) through OprD2 was 2.3 times higher in the presence of mM order of Ca2+, but not Mg2+ or Mn2+. Concomitantly, the intrinsic fluorescence emission of OprD2 became about 10% lower in the presence of Ca2+. As the proteolytic cleavage of the gate-forming domain of OprD2 results the channel activity about 7 times higher, we tested the effect of Ca2+ on the solute permeability through the trypsin-treated OprD2. The diffusion rate of PNPP in the trypsin-treated OprD2 appeared to be nearly identical in the presence and absence of Ca2+. The result suggests that Ca2+ activates the OprD2 channel exerting its effect on the gate-forming domain.
Department of Molecular Life Science, Tokai University School of Medicine, Isehara, Japan.
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Yoshihara
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Nakae
D001425:Bacterial Outer Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D005470:Fluorometry; D015378:Imipenem / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009596:Nitrophenols / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D018272:Porins; D011510:Proteolipids; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D014357:Trypsin / Q000494:pharmacology
D001425:Bacterial Outer Membrane Proteins; D002413:Cations, Divalent; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D018272:Porins; D011510:Proteolipids; C020485:proteoliposomes; C008644:nitrophenylphosphate; D008345:Manganese; D015378:Imipenem; D014357:Trypsin; D008274:Magnesium; D002118:Calcium