Man Dikla, Wang Weiwu, Sabehi Gazalah, Aravind L, Post Anton F, Massana Ramon, Spudich Elena N, Spudich John L, Béjà Oded
Department of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.
EMBO J. 2003 Apr 15;22(8):1725-31. doi: 10.1093/emboj/cdg183.
Proteorhodopsins, ubiquitous retinylidene photoactive proton pumps, were recently discovered in the cosmopolitan uncultured SAR86 bacterial group in oceanic surface waters. Two related proteorhodopsin families were found that absorb light with different absorption maxima, 525 nm (green) and 490 nm (blue), and their distribution was shown to be stratified with depth. Using structural modeling comparisons and mutagenesis, we report here on a single amino acid residue at position 105 that functions as a spectral tuning switch and accounts for most of the spectral difference between the two pigment families. Furthermore, looking at natural environments, we found novel proteorhodopsin gene clusters spanning the range of 540-505 nm and containing changes in the same identified key switch residue leading to changes in their absorption maxima. The results suggest a simultaneous diversification of green proteorhodopsin and the new key switch variant pigments. Our observations demonstrate that this single-residue switch mechanism is the major determinant of proteorhodopsin wavelength regulation in natural marine environments.
视紫质是广泛存在的视黄醛光活性质子泵，最近在海洋表层水的未培养的全球分布的SAR86细菌群中被发现。发现了两个相关的视紫质家族，它们吸收不同最大吸收波长的光，分别为525纳米（绿色）和490纳米（蓝色），并且它们的分布随深度分层。通过结构建模比较和诱变，我们在此报告105位的一个单一氨基酸残基，它作为光谱调谐开关，并且是两个色素家族之间大部分光谱差异的原因。此外，观察自然环境时，我们发现了新的视紫质基因簇，其范围在540 - 505纳米，并且在相同的已确定的关键开关残基处有变化，导致其最大吸收波长发生变化。结果表明绿色视紫质和新的关键开关变体色素同时发生了多样化。我们的观察表明，这种单残基开关机制是自然海洋环境中视紫质波长调节的主要决定因素。
