Govorunova Elena G, Sineshchekov Oleg A, Spudich John L
Center for Membrane Biology and Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas.
Center for Membrane Biology and Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, McGovern Medical School, Houston, Texas.
Biophys J. 2016 Jun 7;110(11):2302-2304. doi: 10.1016/j.bpj.2016.05.001. Epub 2016 May 24.
Microbial rhodopsins are remarkable for the diversity of their functional mechanisms based on the same protein scaffold. A class of rhodopsins from cryptophyte algae show close sequence homology with haloarchaeal rhodopsin proton pumps rather than with previously known channelrhodopsins from chlorophyte (green) algae. In particular, both aspartate residues that occupy the positions of the chromophore Schiff base proton acceptor and donor, a hallmark of rhodopsin proton pumps, are conserved in these cryptophyte proteins. We expressed the corresponding polynucleotides in human embryonic kidney (HEK293) cells and studied electrogenic properties of the encoded proteins with whole-cell patch-clamp recording. Despite their lack of residues characteristic of the chlorophyte cation channels, these proteins are cation-conducting channelrhodopsins that carry out light-gated passive transport of Na(+) and H(+). These findings show that channel function in rhodopsins has evolved via multiple routes.
微生物视紫红质因其基于相同蛋白质支架的功能机制多样性而引人注目。一类隐藻藻类的视紫红质与嗜盐古菌视紫红质质子泵具有密切的序列同源性，而不是与先前已知的绿藻（绿藻门）通道视紫红质。特别是，占据发色团席夫碱质子受体和供体位置的两个天冬氨酸残基，这是视紫红质质子泵的一个标志，在这些隐藻蛋白质中是保守的。我们在人胚肾（HEK293）细胞中表达了相应的多核苷酸，并用全细胞膜片钳记录研究了编码蛋白的电生特性。尽管它们缺乏绿藻阳离子通道特有的残基，但这些蛋白质是阳离子传导通道视紫红质，可进行光门控的Na(+)和H(+)被动运输。这些发现表明视紫红质中的通道功能是通过多种途径进化而来的。
