Even without eyes, many single-celled organisms can perceive and react to light. This is achieved via rhodopsins, proteins at the cell surface that trigger responses to specific wavelengths of light by directing the flow of ions into or out of the cell.
Figure 1: Crystal structure of ARII, a light-activated proton pump from the algae Acetabularia acetabulum. Copyright : 2011 Shigeyuki Yokoyama
Naoki Kamo’s group at Matsuyama University in Ehime recently began working with ARII, a gene encoding a rhodopsin from the algae Acetabularia acetabulum. The encoded ARII protein proved extremely difficult to characterize and its function was initially ambiguous. However, Kamo’s team found success by joining forces with Shigeyuki Yokoyama’s group at the RIKEN Systems and Structural Biology Center in Yokohama.
To reveal a protein’s structure and function, scientists typically generate highly ordered crystals of that protein and then analyze the diffraction pattern that results when the crystals are bombarded with x-rays. Membrane proteins will fold only under very specific conditions, but Yokoyama’s team devised a ‘cell-free’ system that provides tight control over protein manufacture2. By mixing the cellular protein synthesis machinery with lipids and detergents, they were able to achieve an environment highly hospitable to ARII production.
“This tough target could be expressed very efficiently using our cell-free protein synthesis system, even to the same degree as easy, soluble proteins,” says Yokoyama. He was subsequently able to rapidly purify the resulting protein and obtained a high-resolution structure for ARII by crystallizing it in the presence of lipid molecules (Fig. 1).
ARII proved to be relatively similar to bacteriorhodopsin (BR), a proton pump from the archaeal species Halobacterium salinarum. Preliminary analysis of ARII suggested that this protein likewise acts to transport protons from the cytoplasm to the exterior of the cell in response to illumination.
By analyzing the ARII structure, the researchers were able to identify a network of amino acids that directly participate in the uptake and release of individual protons. There are some notable differences in the kinetics of proton transport between BR and ARII. Kamo and Yokoyama also noted subtle structural disparities that might explain why ARII releases its protons ‘late’ relative to the rapid release observed with BR.
Having demonstrated the effectiveness of this membrane protein synthesis approach, the researchers are now delving deeper into the structure and function of ARII and ARI, another rhodopsin expressed by A. acetabulum. “We will produce various mutants with this efficient cell-free system and use many biophysical methods to understand the detailed proton transport mechanism and physiological roles of ARI and ARII,” says Yokoyama.
The corresponding author for this highlight is based at the Systems and Structural Biology Research Team, RIKEN Systems and Structural Biology Center
Wada, T., Shimono, K., Kikukawa, T., Hato, M., Shinya, N., Kim, S.Y., Kimura-Someya, T., Shioruzu, M., Tamogami, J., Miyauchi, S. et al. Crystal structure of the eukaryotic light-driven proton-pumping rhodopsin, Acetabularia rhodopsin II, from marine alga. Journal of Molecular Biology 411, 986–998 (2011). article
Shimono, K., Goto, M., Kikukawa, T., Miyauchi, S., Shirouzu, M., Kamo, N. & Yokoyama, S. Production of functional bacteriorhodopsin by an Eschericihia coli cell-free protein synthesis system supplemented with steroid detergent and lipid. Protein Science 18, 2160–2171 (2009). article
New tool improves beekeepers' overwintering odds and bottom line
19.09.2019 | US Department of Agriculture - Agricultural Research Service
Elusive compounds of greenhouse gas isolated by Warwick chemists
18.09.2019 | University of Warwick
To process information, photons must interact. However, these tiny packets of light want nothing to do with each other, each passing by without altering the...
Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Hamburg and the European Molecular Biology Laboratory (EMBL) outstation in the city have developed a new method to watch biomolecules at work. This method dramatically simplifies starting enzymatic reactions by mixing a cocktail of small amounts of liquids with protein crystals. Determination of the protein structures at different times after mixing can be assembled into a time-lapse sequence that shows the molecular foundations of biology.
The functions of biomolecules are determined by their motions and structural changes. Yet it is a formidable challenge to understand these dynamic motions.
At the International Symposium on Automotive Lighting 2019 (ISAL) in Darmstadt from September 23 to 25, 2019, the Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, a provider of research and development services in the field of organic electronics, will present OLED light strips of any length with additional functionalities for the first time at booth no. 37.
Almost everyone is familiar with light strips for interior design. LED strips are available by the metre in DIY stores around the corner and are just as often...
Later during this century, around 2060, a paradigm shift in global energy consumption is expected: we will spend more energy for cooling than for heating....
Researchers from the Department of Atomically Resolved Dynamics of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg, the University of Potsdam (both in Germany) and the University of Toronto (Canada) have pieced together a detailed time-lapse movie revealing all the major steps during the catalytic cycle of an enzyme. Surprisingly, the communication between the protein units is accomplished via a water-network akin to a string telephone. This communication is aligned with a ‘breathing’ motion, that is the expansion and contraction of the protein.
This time-lapse sequence of structures reveals dynamic motions as a fundamental element in the molecular foundations of biology.
10.09.2019 | Event News
04.09.2019 | Event News
29.08.2019 | Event News
19.09.2019 | Physics and Astronomy
19.09.2019 | Health and Medicine
19.09.2019 | Life Sciences