Ion–peptide interactions between alkali metal ions and a termini-protected dipeptide: modeling a portion of the selectivity filter in K⁺ channels

Abstract

Differentiating K+ and Na+ binding patterns in peptide sequences.

Alkali and Alkaline Earth Metal Ions Complexes with a Partial Peptide of the Selectivity Filter in K+ Channels Studied by a Cold Ion Trap Infrared Spectroscopy

“…IRPD spectra of Ac‐Tyr‐NHMe (GYG)‐alkali metal (M + ) complex are shown in Figure . In the spectra of GYG‐Na + (Figure b) and GYG‐K + (Figure c), bands of C=O stretch and N−H stretch are color‐coded according to the three conformers, O/O, O/O’ and O/O/R, which were assigned in our previous work by applying IR 2 dip spectroscopy with aid of quantum chemistry calculations . In the Amide A region associated with N−H stretches, the bands of the Na + complex, observed at 3429 cm −1 and 3423 cm −1 , were assigned to O/O (green), while the band at 3410 cm −1 was assigned to O/O’ (red).…”

“…M=Li (a), Na (b), K (c), Rb (d), and Cs (e). IRPD spectra of Na + and K + complexes are taken from a previous paper . The assignments of O/O, O/O’, and O/O/R are colored by green, red, and blue, respectively.…”

“…By scanning the frequency of the IR laser, IR photodissociation (IRPD) spectra were measured. To measure the IR spectra of a specific cluster ion conformer, IR‐IR (IR 2 dip) spectroscopy was employed . In this method, a second tunable IR laser (LaserVision) was used.…”

“…BSSE correction was not used because we compared the relative energies (not the absolute energy) of different conformers in the same metal ion – GYG complex. The initial structures were referred from our previous report . The harmonic frequencies were scaled by linear scaling factors: 0.956 for OH and NH stretching regions and 0.975 for others .…”

“…To investigate such a local interaction at the molecular level, the bottom‐up approach is a reasonable and insightful technique . Our previous bottom‐up approach for the partial Ac‐Tyr‐NHMe (GYG) peptide of the selectivity filter and metal cations (K + and Na + ) gave a clear interpretation for this question . The dipeptide Ac‐Tyr‐NHMe, where N‐terminus (−NH 2 ) and C‐terminus (−COOH) were replaced with hydrogen atoms, replicates GYG sequence (see Figure S2).…”