In a recent study published in The Plant Journal, Michigan State University researchers have shown how the two parts of the orange carotenoid protein, or OCP, interact by splitting the native protein into its two building blocks.
The OCP is found in cyanobacteria, organisms that are prodigiously productive at photosynthesis. It protects its host from damage caused by exposure to too much sunlight.
The protein is made out of two building blocks, C-terminal domain and N-terminal domain, spanned by a carotenoid pigmentthat bolts the two parts together.
Sigal Lechno-Yossef, a postdoctoral researcher in the lab of Cheryl Kerfeld at the MSU Department of Energy Plant Research Laboratory, and her colleagues wanted to understand how the two building blocks interact. They had suspected that the modern OCP is the result of ancestors of the two domains joining together, millions of years ago.
“Our lab wanted to better understand the evolution process of the OCP from domain homologs found in cyanobacteria today,” Lechno-Yossef said.
The team reversed this evolutionary event in the lab by breaking down the connecting carotenoid bond to split apart an OCP protein. They put both domains into a test host to see if they would find each other and connect again, essentially retracing the steps they think were made during the evolutionary process.
“Without carotenoid, the two parts stayed separate,” Lechno-Yossef said. “Once we put in the carotenoid, they latched onto each other. We basically created multiple synthetic versions of the OCP.”
The synthetic OCPs were similar to their natural cousins in how they reacted in the presence of light. For some reason, probably in the fine details of their structures, only one of the synthetic versions functioned similarly in the dark.
Kerfeld thinks that precise knowledge of the structures of the various OCP building blocks makes them especially susceptible to engineering.
The long-term goal is to use the OCP and its separate subcomponents in new, synthetic systems, specifically optogenics, a recently developed approach that uses light to control processes in living cells.
Optogenetics is showing us how the brain works, and scientists hope that targeting specific brain cells will help us cure Parkinson’s or Alzheimer’s, even combat mental illnesses.
Light-sensitive proteins, like the OCP, are key to activating and controlling events in optogenetic applications. Although the OCP has yet to be tried in an optogenetic application, the team thinks their properties make them likely to be useful.
“OCPs respond faster to light, compared to the current light-sensitive proteins used in optogenetic experiments, and now that we’ve shown we can make artificial hybrid OCPs, we have a wider range of application options,” Lechno-Yossef said. “We are still in the theoretical phase of imagining applications, but we are not far from where we can start experimenting with synthetic systems.”
