Back Cover: Early Formation of the Ion‐Conducting Pore in Channelrhodopsin‐2 (Angew. Chem. Int. Ed. 16/2015)

Abstract

The light-gated ion channel … …c hannelrhodopsin-2 (ChR 2 )i st he key protein in optogenetics.I nt heir Communication on page 4953 ff., K. Gerwert et al. elucidate channel opening at amolecular level by ac ombination of time-resolved FTIR spectroscopy and molecular dynamics simulations.

Pre-Gating Conformational Changes in the ChETA Variant of Channelrhodopsin-2 Monitored by Nanosecond IR Spectroscopy

“…Recently, the band at 1760 cm −1 was assigned instead to the CO stretch of E123. 18 However, a broad positive band at ∼1760 cm −1 is still observed in the early microseconds of ChR2-E123T ( Figure S10, Supporting Information). Albeit showing half the intensity as that in ChR2-WT, the persistence of this band in the E123T variant is at odds with its assignment to E123.…”

“…This kinetic alteration in the E123T variant might explain why the band at 1760 cm −1 was recently misassigned to E123. 18 How pre-gating structural and protonation changes are linked to the opening of the channel and the onset of cation permeation remains elusive in full atomistic detail, and will require further studies. However, the distortion of helices by retinal isomerization, followed by changes in interhelical interactions and continued by changes in H-bonding networks induced by protonation changes, are likely key elements for the coupling between retinal isomerization and the conformational changes required to form the conductive state.…”

“…During the review of the present manuscript, a nanosecond step-scan FT-IR experiment on ChR2 was presented. 18 However, the conformational changes taking place in the nanoseconds and early microseconds remain largely unexplored by structurally sensitive methods.…”

“…However, these studies have been mostly limited to steady-state FT-IR experiments at liquid nitrogen temperature. , More recently, an ultrafast Vis-pump/IR-probe study and a time-resolved step-scan FT-IR study, covering the picosecond and microsecond range, respectively, have also reported pre-gating structural changes. During the review of the present manuscript, a nanosecond step-scan FT-IR experiment on ChR2 was presented . However, the conformational changes taking place in the nanoseconds and early microseconds remain largely unexplored by structurally sensitive methods.…”

Functional Mechanism of Channelrhodopsins

“…，矢印) ．この初期ピーク電流が元の大きさ に回復するまでには 1 分から 2 分程度，暗状態を保つ必 要がある (Fig.3 (c) Fig.3 (a) (Fig.3 (a) ) ，チャネル閉時間，ま た光順応 (Fig.3 (b) ，矢印) 等の性質をすべて踏まえる と，チャネル開⇔チャネル閉という 2 つの種の単純な反 応スキームで表すことができない．また他の電位依存性 イオンチャネルのようにチャネル開，チャネル閉，不活 性化状態という 3 つの状態を考えるとどうだろうか？ 3 つ目の不活性化状態を考えたとしても数十ミリ秒の早い 不活性化と数十秒もかかる光順応からの回復を同時に説 明することができない．この反故を解消するために様々 なモデルが検証された末，2 つの閉状態 (C1, C2) と 2 つ の開状態 (O1 と O2) を持つ Fig.3 (d 29,[53][54][55][56][57][58] ．チャネルが開く際の構造変化モデルを Fig.4 に示す． 光吸収により all-trans retinal が 13-cis retinal に異性化 する (Fig.4 (a) , 4 (b) (Fig.4 (c) ) ．実際光照射にともなうへ リックス 2 とへリックス 7 のアレンジメントの変化が電 子顕微鏡により観察され，加えて光照射によりこれらへ リックスのフレキシビリティーが上昇するという結果も 報告された 54,58) ． また，レチナール近傍に存在する C128 と D156 は水 素結合を形成しチャネル開閉に関わると示唆されてい る (Fig.4 (a) , DC-gate) 59…”