A team that included Johns Hopkins materials scientists has uncovered new insights into the structure of TrkB, an important protein that helps brain cells grow and adapt.
Their work, which appears in Nature Communications, could help scientists develop more effective drugs for conditions ranging from depression and post-traumatic stress disorder (PTSD) to cancer.
“We already knew that TrkB is a protein found in cell membranes in the brain that aid with cell growth and function, and when it’s working, it dimerizes – coming together and forming pairs,” says team member Daniel McKenzie, a doctoral student in the Whiting School of Engineering’s Department of Materials Science and Engineering. “Our research discovered that a specific part of TrkB, the transmembrane helix, plays a key role in turning it on.”
Researchers studied the interactions of TrkB with fluoxetine, also known as Prozac, because it binds to the transmembrane helix of TrkB.
“We found that when fluoxetine attaches to TrkB, the protein is in its “active” state, indicating that it could start a chain of reactions in the brain to possibly treat mental health conditions,” says McKenzie.
Based on their previous knowledge about the protein, McKenzie and adviser Kalina Hristova, a professor of materials science and engineering and core researcher at Johns Hopkins Institute for NanoBioTechnology, and collaborators from Italy, Spain, and Russia, aimed to investigate receptor interactions to better understand how TrkB functions when it binds to antidepressants.
McKenzie and Hristova’s portion of the study builds on investigations by team member Konstantin S. Mineev, a principal investigator at the Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry in Russia, who used nuclear magnetic resonance (NMR) spectroscopy to identify eight key amino acids in TrkB’s transmembrane helix dimer that appear crucial for dimerization. Also foundational to the work was Marçal Vilar, a principal investigator at the Valencia Biomedical Research Foundation in Spain, whose team confirmed these amino acids’ importance by showing that individual mutations at these sites impaired the receptor’s response. If a mutated TrkB did not work as well as the normal one, researchers inferred that the amino acid was important for its function.
“One amino acid, serine, was found to be important because when it was mutated at position 441, TrkB’s activity appeared to decrease or stop completely,” says McKenzie. “We used a technique called number and brightness to investigate this phenomenon further and found that the mutation didn’t stop TrkB from dimerizing – it was in an inactive state but still formed pairs.”
Typically, the activation of the receptor and the dimerization are processes that are linked. A mutation that prevents activation but still allows the receptors to pair up is unusual and presents new research possibilities, the investigators say.
“A single amino acid out of 800 inactivating the receptor is quite rare, especially because it is located in the transmembrane domain which is largely considered to be unimportant for signaling,” says McKenzie.
The team’s next step is to test TrkB’s response to other antidepressant medications and psychoactive substances, like LSD, to hopefully understand how the functions of TrkB is affected by antidepressants. Scientists are still uncertain if TrkB can be a target of other medications to treat mental health challenges.
“These are difficult questions to tackle, and we will continue working with structural biologists and biochemists to move forward,” says Hristova.
This study was led by researchers from Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, CNR Neuroscience Institute, and the Valencia Biomedical Research Foundation.