Researchers used groundbreaking technology to observe an "important cellular" gatekeeper in its most natural state.
The team looked at G protein-coupled receptors (GPCRs), which are associated with human health; about 40 percent of modern medicines "target" these proteins, a Scripps Research Institute (TSRI) news release reported.
"For the first time we have a room-temperature, high-resolution structure of one of the most difficult-to-study but medically important families of membrane proteins," Vadim Cherezov, a structural biologist at TSRI who led the research, said. "And we have validated this new method so that it can be confidently used for solving new structures."
The team studied serotonin receptors, which influence factors such as human mood and are targeted in "obesity, depression, and migraine" treatments.
They created "crystallized samples of the receptor in a fatty gel that mimics its environment in the cell."
The scientists used a Linac Coherent Light Source (LCLS) laser and a unique "injection system" that "streams" gel into the X-ray pulse; the gel bumps into crystals and creates a 3D model of the serotonin receptor.
In the past researchers have had a hard time growing G protein crystals that were large enough for X-ray studies at synchrotrons. LCLS is a "billion times brighter" than synchrotrons and provides extremely quick snapshots, allowing the researchers to observe the tiny crystals.
"This is one of the niches that LCLS is perfect for," SLAC Staff Scientist Sébastien Boutet, a co-author of the report, said. "With really challenging proteins like this you often need years to develop crystals that are large enough to study at synchrotron X-ray facilities."
"It's a big advantage that you don't have to harvest individual crystals-you can just load the whole gel-like sample with embedded microcrystals in the injector and start collecting data. It's also significant that the crystals don't have to be cryo-cooled in liquid nitrogen to protect them from radiation damage. Instead of looking at the samples at minus 173 degrees Celsius, we can look at them at room temperature-much closer to the temperature of their natural environment, which is body temperature," Wei Liu, a TSRI staff scientist who was first author of the study, said.
Researchers have studied human serotonin receptors in the past, but only when they were frozen; and the process took months to complete. This new method can be carried out in a manner of days.
GPR studies could help make breakthroughs in treatment for conditions like "hypertension, asthma, schizophrenia and Parkinson's disease."
Researchers have now mapped out 800 human GPCRs.
"I view these recent experiments as just the beginning," Cherezov said. "Now it is time to start making a serious impact on the field of structural biology of G protein-coupled receptors and other challenging membrane proteins and complexes. The pace of structural studies in this field is breathtaking, and there is still a lot unknown."
