期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 293, 期 18, 页码 6969-6984出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.RA118.001817
关键词
potassium channel; metal ion-protein interaction; infrared spectroscopy (IR spectroscopy); biophysics; Fourier transform IR (FTIR); ion channel; molecular dynamics; quantum chemistry; fluorescence
资金
- Japan Society for the Promotion of Science KAKENHI [25840122, 17K15109, 16H00778, 16KT0165, 17K05757, 22247024, 22770159, 24650203, 26640047, 26708002]
- NINS program for cross-disciplinary study
- Cooperative Study Program of National Institute for Physiological Sciences
- JST CREST [JPMJCR17N5]
- Grants-in-Aid for Scientific Research [16KT0165, 17H04021, 17K05757] Funding Source: KAKEN
Canonical K+ channels are tetrameric and highly K+-selective, whereas two-pore-domain K+ (K2P) channels form dimers, but with a similar pore architecture. A two-pore-domain potassium channel TWIK1 (KCNK1 or K2P1) allows permeation of Na+ and other monovalent ions, resulting mainly from the presence of Thr-118 in the P1 domain. However, the mechanistic basis for this reduced selectivity is unclear. Using ion-exchange-induced difference IR spectroscopy, we analyzed WT TWIK1 and T118I (highly K+-selective) and L228F (substitution in the P2 domain) TWIK1 variants and found that in the presence of K+ ions, WT and both variants exhibit an amide-I band at 1680 cm(-1). This band corresponds to interactions of the backbone carbonyls in the selectivity filter with K+, a feature very similar to that of the canonical K+ channel KcsA. Computational analysis indicated that the relatively high frequency for the amide-I band is well explained by impairment of hydrogen bond formation with water molecules. Moreover, concentration-dependent spectral changes indicated that the K+ affinity of the WT selectivity filter was much lower than those of the variants. Furthermore, only the variants displayed a higher frequency shift of the 1680-cm(-1) band upon changes from K+ to Rb+ or Cs+ conditions. High-speed atomic force microscopy disclosed that TWIK1's surface morphology largely does not change in K+ and Na+ solutions. Our results reveal the local conformational changes of the TWIK1 selectivity filter and suggest that the amide-I bands may be useful molecular fingerprints for assessing the properties of other K+ channels.
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