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
Molecular motors run in unison in a metal-organic framework
20.03.2019 | University of Groningen
Active substance from plant slows down aggressive eye cancer
20.03.2019 | Rheinische Friedrich-Wilhelms-Universität Bonn
Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.
Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...
The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.
A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...
Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.
"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...
New research group at the University of Jena combines theory and experiment to demonstrate for the first time certain physical processes in a quantum vacuum
For most people, a vacuum is an empty space. Quantum physics, on the other hand, assumes that even in this lowest-energy state, particles and antiparticles...
Physicists in the EPic Lab at University of Sussex make crucial development in global race to develop a portable atomic clock
Scientists in the Emergent Photonics Lab (EPic Lab) at the University of Sussex have made a breakthrough to a crucial element of an atomic clock - devices...
11.03.2019 | Event News
01.03.2019 | Event News
28.02.2019 | Event News
20.03.2019 | Life Sciences
20.03.2019 | Life Sciences
20.03.2019 | Trade Fair News