Among others, it possesses a rhodopsin protein in its cell membrane which carries chloride anions from outside the cell to its inside. Researchers now gained in-depth insight into how the chloride pump in Nonlabens marinus works.
Pink crystals reveal the mechanism of chloride transportation over the cell membrane: Using time-resolved serial crystallography, the pink NmHR crystals revealed ion binding sites in the chloride transporter and pumping dynamics after photoactivation. As the study has revealed, the chloride anion is attracted by a positively charged patch of the rhodopsin protein in Nonlabens marinus cell membrane. When retinal isomerizes due to light direct exposure and flips over, it drags the chloride anion along and therefore transfers it a bit more inside the protein.
Photoactive chloride pumping through the cell membrane caught by time-resolved serial crystallography: Chloride ions (green spheres) are transferred throughout the cell membrane by the NmHR chloride pump (pink). Credit: Guillaume Gotthard, Sandra Mous
For the very first time, a molecular film has recorded in detail the process of an anion transported across the cell membrane by a light-fuelled protein pump. Publishing in Science, the researchers have actually unraveled the mystery of how light energy initiates the pumping procedure– and how nature made sure there is no anion leakage back outside.
Many germs and unicellular algae have light-driven pumps in their cell membranes: proteins that change shape when exposed to photons such that they can transport charged atoms in or out of the cell. Thanks to these pumps, their unicellular owners can adjust to the environments pH worth or salinity.
One such bacteria is Nonlabens marinus, first discovered in 2012 in the Pacific Ocean. To name a few, it has a rhodopsin protein in its cell membrane which transfers chloride anions from outside the cell to its within. Just like in the human eye, a retinal particle bound to the protein isomerizes when exposed to light. This isomerization begins the pumping process. Researchers now gained in-depth insight into how the chloride pump in Nonlabens marinus works.
The research study was led by Przemyslaw Nogly, once a postdoc at PSI and now an Ambizione Fellow and Group Leader at ETH Zürich. With his team, he combined experiments at 2 of PSIs large-scale research study centers, the Swiss Light Source SLS and the X-ray free-electron laser SwissFEL. Slower dynamics in the millisecond-range were investigated through time-resolved serial crystallography at SLS while quicker, approximately picosecond, events were captured at SwissFEL– then both sets of data were put together.
Pink crystals reveal the system of chloride transportation over the cell membrane: Using time-resolved serial crystallography, the pink NmHR crystals revealed ion binding sites in the chloride transporter and pumping characteristics after photoactivation. This enabled researchers to decipher the chloride transportation mechanism. Credit: Sandra Mous
” In one paper, we make use of the benefits of two modern facilities to inform the complete story of this chloride pump,” Nogly states. Jörg Standfuss, co-author of the study who developed up a PSI group committed to developing such molecular films, adds: “This combination allows first-class biological research study as would just be possible at really few other places worldwide beside PSI.”
No backflow
As the research study has actually exposed, the chloride anion is drawn in by a favorably charged spot of the rhodopsin protein in Nonlabens marinus cell membrane. When retinal isomerizes due to light direct exposure and turns over, it drags the chloride anion along and thus transports it a bit additional inside the protein.
Being on the opposite of the retinal molecule now, the chloride ion has actually reached a moment of truth. From here, it goes only additional inside the cell. An amino acid helix also unwinds when chloride moves along, furthermore blocking the passage back outdoors. “During the transportation, two molecular gates therefore make certain that chloride just moves in one direction: within,” Nogly says. One pumping process in total takes about 100 milliseconds.
2 years earlier, Jörg Standfuss, Przemyslaw Nogly and their group unravelled the system of another light-driven bacterial pump: the sodium pump of Krokinobacter eikastus. Researchers aspire to discover the details of light-driven pumps due to the fact that these proteins are important optogenetic tools: genetically crafted into mammalian neurons, they make it possible to control the neurons activities by light and therefore research their function.
Recommendation: “Dynamics and mechanism of a light-driven chloride pump” by Sandra Mous, Guillaume Gotthard, David Ehrenberg, Saumik Sen, Tobias Weinert, Philip J. M. Johnson, Daniel James, Karol Nass, Antonia Furrer, Demet Kekilli, Pikyee Ma, Steffen Brünle, Cecilia Maria Casadei, Isabelle Martiel, Florian Dworkowski, Dardan Gashi, Petr Skopintsev, Maximilian Wranik, Gregor Knopp, Ezequiel Panepucci, Valerie Panneels, Claudio Cirelli, Dmitry Ozerov, Gebhard Schertler, Meitian Wang, Chris Milne, Joerg Standfuss, Igor Schapiro, Joachim Heberle and Przemyslaw Nogly, 3 February 2022, Science.DOI: 10.1126/ science.abj6663.