Researchers have developed a tool that effectively maps the critical interactions that influence how drugs work within a specific superfamily of cell receptors.
About one-third of the drugs approved by the FDA target a major superfamily of receptors located on human cell surfaces. These vital medications, ranging from beta blockers to antihistamines, initiate complex biochemical processes through these receptors, which can prevent heart attacks or rapidly address allergic reactions.
However, scientists have discovered that the situation is more intricate than previously thought, with many of these drugs actually affecting a structure made up of one receptor coupled with one associated protein. A recent study published in Science Advances presents a groundbreaking method for mapping the interactions between 215 of these receptors and the three proteins they associate with. These results significantly enhance our comprehension of these interactions and their potential therapeutic applications.
“From a technical standpoint, we can now examine these receptors on a level of detail we never had before,” says Ilana Kotliar, the study’s lead author and a former PhD student in Rockefeller’s Laboratory of Chemical Biology and Signal Transduction, led by Thomas P. Sakmar. “Biologically, we’ve discovered that the interaction between proteins and receptors occurs far more widely than we had realized, paving the way for future explorations.”
Exploring New Frontiers
This group of receptors is known as GPCRs, or G protein-coupled receptors, while their partner proteins are referred to as RAMPs, which stands for receptor activity-modifying proteins. RAMPs assist in transporting GPCRs to the cell surface and can significantly modify how these receptors convey signals by altering the receptor’s configuration or affecting its position. Because GPCRs seldom function independently, recognizing a GPCR without considering the impact of RAMPs is akin to knowing the menu of a restaurant without checking its operating hours or location.
“It’s possible to have two cells in the body where the same drug targets the same receptor, yet the drug may be effective in only one of those cells,” explains Sakmar, the Richard M. and Isabel P. Furlaud Professor. “The distinction lies in whether one of those cells has a RAMP that transports its GPCR to the surface, where the drug can interact with it. That’s why RAMPs are crucial.”
With this knowledge, Sakmar and his team were eager to devise a method to elucidate the effect of each RAMP on every GPCR. Constructing such an extensive map of GPCR-RAMP interactions could significantly enhance drug development and might also clarify why certain promising GPCR-targeted drugs have unexpectedly failed to perform.
They also hoped this map would contribute to fundamental biology by uncovering the natural ligands that interact with several so-called “orphan” GPCRs. “There are still many GPCRs in the human body whose activators remain a mystery,” Kotliar explains. “Previous screenings might have overlooked those connections because they did not consider the GPCR-RAMP complex.”
However, sifting through all GPCR-RAMP interactions proved to be a challenging endeavor. With three known RAMPs and nearly 800 GPCRs, exploring every potential combination was impractical. In 2017, Emily Lorenzen, then a graduate student in Sakmar’s lab, initiated a partnership with researchers from Sweden’s Science for Life Laboratory and the Human Protein Atlas Project to develop a test capable of screening GPCR-RAMP interactions.
Conducting Hundreds of Experiments Simultaneously
The research team began by linking antibodies from the Human Protein Atlas to magnetic beads, each colored with one of 500 different dyes. These beads were then placed in a liquid containing engineered cells that expressed various combinations of RAMPs and GPCRs. This innovative method allowed researchers to simultaneously investigate hundreds of potential GPCR-RAMP interactions in a single experiment. As each bead moved through a detection device, the color coding helped identify which GPCRs were bound to which RAMPs, enabling high-throughput analysis of 215 GPCRs and their interactions with the three known RAMPs.
“Most of this technology was already in place; our contribution was to enhance it,” noted Sakmar. “We established a method to test hundreds of different complexes at once, generating massive amounts of data and answering numerous questions simultaneously.”
“Typically, researchers don’t think in terms of multiplexing. But that’s precisely what we accomplished — conducting 500 experiments at the same time.”
While this achievement was the result of a collaborative effort over an extended period, Kotliar worked exceptionally hard to ensure its success, transporting samples and scarce materials back and forth from Sweden during limited travel windows amid COVID.
Her dedication paid off. The results yielded valuable resources for GPCR researchers and drug developers: publicly accessible online databases of anti-GPCR antibodies, engineered GPCR genes, and, of course, the mapped interactions. “Now you can search for your preferred receptor, see which antibodies bind to it, find out if those antibodies are commercially available, and learn if that receptor interacts with a RAMP,” explains Sakmar.
The findings have greatly increased the number of experimentally verified GPCR-RAMP interactions and provide a foundation for techniques that may help detect combinations of GPCRs and identify harmful autoantibodies. “In essence, this is a technology-centered project,” Sakmar concludes. “That’s the focus of our lab. We aim to develop technologies that further drug discovery.”
