Table 2.

Normal modes of the carbonyl groups in the selectivity filter of TWIK1 (five highest IR absorbance intensities)

TWIK1 [S0, S2, S4]			TWIK1 [S1, S3]
Frequency	Intensity of IR absorbance	Contribution to the modea	Frequency	Intensity of IR absorbance	Contribution to the mode
cm−1		%	cm−1		%
1708	14.6	21 (1.5A), 17 (2.5A), 11 (0.5A)	1711	20.0	18 (0.5B′), 6 (0.5A′), 4 (1.5B′)
1719	11.9	64 (0.5A′)	1717	14.3	16 (0.5A′), 9 (0.5B), 6 (0.5A)
1713	11.7	31 (2.5B), 16 (3.5A), 10 (3.5B)	1706	13.1	14 (0.5A), 8 (2.5A), 8 (0.5B′)
1728	10.5	56 (0.5B), 4 (0.5B′)	1698	9.4	23 (2.5A′), 21 (2.5B′), 6 (3.5B′)
1703	9.5	43 (0.5A), 6 (2.5A′), 4 (1.5A′)	1730	6.5	31 (0.5B), 3 (0.5A′), 3 (0.5B′)

^a The number indicates the position of the carbonyl groups according to the K⁺-binding site number. 1.5 indicates a carbonyl group between S1 and S2 sites. A and B correspond to each monomer of TWIK1, which are colored orange and sky blue, respectively, in Fig. 7. A′ and B′ indicate the P2 domain.