Molecular Determinants Differentiating Photocurrent Properties of Two Channelrhodopsins from Chlamydomonas
Molecular Determinants Differentiating Photocurrent Properties of Two Channelrhodopsins from Chlamydomonas
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DOI：
10.1074/jbc.m807632200
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发表时间：
2009-02-27
影响因子：
4.8
通讯作者：
Yawo, Hiromu
中科院分区：
文献类型：
--
作者：
Wang, Hongxia;Sugiyama, Yuka;Yawo, Hiromu
光信号在一种叫做通道视紫红质的分子中转化为电信号，通道视紫红质是单细胞绿藻中的一种古菌型视紫红质。虽然高度同源，但该家族的两个分子，通道视紫红质-1 （ChR1）和-2 (ChR2)，在光电流性质上是不同的，如波长敏感性，脱敏性和打开和关闭动力学。然而，调节这些特性的结构尚未完全确定。用ChR1的同源对应物取代ChR2的n端片段制成的嵌合体分子，对其光电流进行了分析。我们发现光电流的波长敏感性发生了红移，但脱敏作用可以忽略不计，当用含有ChR1第5跨膜螺旋的片段替换时，光电流的开启和关闭动力学减慢。因此，这一环节涉及到测定光电流性质、波长灵敏度以及表征ChR1和ChR2的动力学。分别交换了8个氨基酸残基，并进一步分析了每个靶向突变体ChR2的光电流特性。其中Tyr226(ChR1)/Asn187（ChR2）的位置是参与波长敏感性、脱敏和开启和关闭动力学的分子决定因素之一。这表明这些氨基酸残基直接或间接地与发色团以及决定光电流动力学的蛋白质结构相互作用。一些嵌合体通道视紫红质被认为比野生型ChR2在引入光诱导膜去极化以人工刺激体内神经元和视觉假体以治疗光感受器变性方面具有一些优势。
A light signal is converted into an electrical one in a single molecule named channelrhodopsin, one of the archaea-type rhodopsins in unicellular green algae. Although highly homologous, two molecules of this family, channelrhodopsin-1 (ChR1) and -2 (ChR2), are distinct in photocurrent properties such as the wavelength sensitivity, desensitization, and turning-on and -off kinetics. However, the structures regulating these properties have not been completely identified. Photocurrents were analyzed for several chimera molecules made by replacing N-terminal segments of ChR2 with the homologous counterparts of ChR1. We found that the wavelength sensitivity of the photocurrent was red-shifted with negligible desensitization and slowed turning-on and -off kinetics when replacement was made with the segment containing the fifth transmembrane helix of ChR1. Therefore, this segment is involved in the determination of photocurrent properties, the wavelength sensitivity, and the kinetics characterizing ChR1 and ChR2. Eight amino acid residues differentiating this segment were exchanged one-by-one, and the photocurrent properties of each targeted mutant ChR2 were further analyzed. Among them, position Tyr226(ChR1)/Asn187(ChR2) is one of the molecular determinants involved in the wavelength sensitivity, desensitization, and turning-on and -off kinetics. It is suggested that these amino acid residues directly or indirectly interact with the chromophore as well as with the protein structure determining the photocurrent kinetics. Some of the chimera channelrhodopsins are suggested to have several advantages over the wild-type ChR2 in the introduction of light-induced membrane depolarization for the purpose of artificial stimulation of neurons in vivo and visual prosthesis for photoreceptor degeneration.