For approximately 3.5 billion years, solar light has been the main energy source for all life forms on Earth. Therefore, the ability of proteins to capture solar rays and convert them into usable forms of energy is a "natural" development of all living systems. The Dead Sea is one of the most saline lakes on Earth, and few microorganisms are found in its waters. Among these microorganisms, the haloarchaeon (a salt-loving archaea) Haloarcula marismortui survives such harsh conditions by adopting a unique six-rhodopsin system (1). Thee six rhodopsins, often called microbial rhodopsins, are activated by different wavelengths of sun rays and function in light energy harvest and phototaxis. More than 1000 microbial rhodopsins have been identified in bacteria, eukaryotes and archaea. The rhodopsin involved in capturing light for biological usage is called bacteriorhodopsin. Bacteriorhodopsin is a light-driven outward proton pump. Upon light activation, it pumps a proton pre-bound in the interior of the protein and re-uptakes another from inside the cell. This process can be carried out repeatedly every ~10 msec. The protons accumulated outside will then re-enter the cell through another protein called F1Fo ATP synthase. Every three protons that reenter will trigger the generation of one ATP, a universal, biologically consumable form of energy. Ultimately, haloarchaea can harvest energy via exposure to sun rays. A study conducted in the lab of professor Chii-Shen Yang at the College of Life Science unveiled a new kind of bacteriorhodopsin (2) that is at least ten times more powerful than any currently known bacteriorhodopsin in pumping protons outside of the cell. Yang's lab further worked with a research group in Academia Sinica and resolved the atomic structure of this new bacteriorhodopsin. These researchers found a cap-like structure that faced the outside of the cell and was stabilized by some extra chemical bonding networks, leading to functional enhancement. This research will be noted as an important milestone for the application of such microbial rhodopsins because it provides a lucid principle for future protein engineering to improve the functionality of such proteins. In this study, Yang's lab used this powerful bacteriorhodopsin to develop an ITO-based device (3) and showed that measurable electric current could be produced upon light activation. This device provides new design possibilities for the development of medical and electronic applications of bacteriorhodopsins. References 1. Hsu-Yuan Fu, Yu-Cheng Lin, Yung-Ning Chang, Hsiaochu Tseng, Ching-Che Huang, Kang-Cheng Liu, Ching-Shin Huang, Che-Wei Su, Rueyhung Roc Weng, Yin-Yu Lee, Wailap Victor Ng, and Chii-Shen Yang. (2010). A novel six-rhodopsin system in a single archaeon. Journal of Bacteriology, 192(22), 5866-73. DOI: 10.1128/JB.00642-10 2. Min-Feng Hsu, Hsu-Yuan Fu, Chun-Jie Cai, Hsiu-Pin Yi, Chii-Shen Yang, and Andrew H.-J. Wang. (2015). Structural and Functional Studies of a Newly Grouped Haloquadratum walsbyi Bacteriorhodopsin Reveal the Acid-resistant Light-driven Proton Pumping Activity. Journal of Biological Chemistry, 290(49), 29567-77. DOI: 10.1074/jbc.M115.685065 3. Hsu-Yuan Fu, Hsiu-Ping Yi, Yen-Hsu Lu, Chii-Shen Yang. (2013). Insight into a single halobacterium using a dual-bacteriorhodopsin system with different functionally optimized pH ranges to cope with periplasmic pH changes associated with continuous light illumination. Molecular Microbiology, 88(3), 551-61. Associate Professor Chii-Shen Yang Department of Biochemical Science and Technology chiishen@ntu.edu.tw References 1. Hsu-Yuan Fu, Yu-Cheng Lin, Yung-Ning Chang, Hsiaochu Tseng, Ching-Che Huang, Kang-Cheng Liu, Ching-Shin Huang, Che-Wei Su, Rueyhung Roc Weng, Yin-Yu Lee, Wailap Victor Ng, and Chii-Shen Yang. (2010). A novel six-rhodopsin system in a single archaeon. Journal of Bacteriology, 192(22), 5866-73. DOI: 10.1128/JB.00642-10 2. Min-Feng Hsu, Hsu-Yuan Fu, Chun-Jie Cai, Hsiu-Pin Yi, Chii-Shen Yang, and Andrew H.-J. Wang. (2015). Structural and Functional Studies of a Newly Grouped Haloquadratum walsbyi Bacteriorhodopsin Reveal the Acid-resistant Light-driven Proton Pumping Activity. Journal of Biological Chemistry, 290(49), 29567-77. DOI: 10.1074/jbc.M115.685065 3. Hsu-Yuan Fu, Hsiu-Ping Yi, Yen-Hsu Lu, Chii-Shen Yang. (2013). Insight into a single halobacterium using a dual-bacteriorhodopsin system with different functionally optimized pH ranges to cope with periplasmic pH changes associated with continuous light illumination. Molecular Microbiology, 88(3), 551- 61. Associate Professor Chii-Shen Yang Department of Biochemical Science and Technology chiishen@ntu.edu.tw