title: pH-dependent promotion of phospholipid flip-flop by the KcsA  potassium channel.
abstract: KcsA is a pH-dependent potassium channel that is activated at acidic pH. The channel undergoes global conformational changes upon activation. We hypothesized that the open-close conformational changes of the transmem brane region could promote the flip-flop of phosphoiipids. Based on this hypothesis, we measured the flip-flop ofNBD-labeled phospholipids in KcsA-incorporated proteoliposomes. Both flip and flop rates of ~NBD-PC were significantly enhanced in the presence of KcsA and were several times higher at pH 4.0 than at pH 7.4, suggesting that KcsA promotes the phospholipid flip in a conformation-dependent manner. Phospholipids were nonselectively flipped with respect to the glycerophospholipid structure. In the active state of KcsA channel,tetrabutylammonium locks the channel in the open conformation at acidic pH; however, it did not alter the fliprate of CGNBD-PC. Thus, the open-close transition of the transmembrane region did not affect the flip-flop of phospholipids. In addition, the KcsA mutant that lacked anN-terminal amphipathic helix (MO-helix) was found to show reduced ability to fl ip C6NBD-phospholipids at acidic pH. The closed conformation is stabilized in the absence of MO-heli x, and thus the attenuated flip could be explained by the reduced prevalence of the open conformation.These results suggest that the open conformation of KcsA can disturb the bilayer integrity and facilitate the flip-flop of phospholipids.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nakao
authors.forename: Keisuke
authors.initials: K
authors.lastname: Ikeda
authors.forename: Masayuki
authors.initials: M
authors.lastname: Iwamoto
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Shimizu
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Oiki
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ishihama
authors.forename: Minoru
authors.initials: M
authors.lastname: Nakano
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives / Q000737:chemistry; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002784:Cholesterol / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009154:Mutation; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D010743:Phospholipids / Q000737:chemistry* / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
chemical_list: C078632:1-acyl-2-(12-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl)phosphatidylcholine; D001426:Bacterial Proteins; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010743:Phospholipids; D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; C107790:prokaryotic potassium channel; D002784:Cholesterol; C009405:tetrabutylammonium; D009327:4-Chloro-7-nitrobenzofurazan; C028694:1-palmitoyl-2-oleoylphosphatidylcholine