Scientists at the Goethe and Leipzig Universities in Germany have developed a new method to direct the assembly of receptors on the surface of living cells, using light. The scientists showed that a group of G protein-coupled receptors (GPCRs), “confined” under a beam of light on the cell’s surface, can initiate downstream signaling just as when the GPCR binds its ligand, neuropeptide Y.
“The serendipity about this experiment is that the clustering of receptors triggers a signal that is similar to that of neuropeptide Y. Solely by the clustering, we were able to trigger cell movement as a reaction of the cell. The laser spots even allowed us to control the direction of the cell movement,” said Robert Tampé, PhD, professor of biochemistry, Institute of Biochemistry at Goethe University, Frankfurt, and senior author on the study.
Light-sensitive lock-and-key pairs are very small compared to the size of the receptor molecules. This allows the scientists to precisely control the organization of the receptors in the cell membrane using the laser spot.
“This noninvasive method is thus particularly well suited to study the effects of receptor clustering in living cells,” said Tampé. “Our method can be used to investigate exciting scientific questions, such as how receptors are organized in networks and how new circuits are formed in the brain.”
The functional organization of the 100 trillion cells that make up a human body requires constant communication among cells and the environment. Signals abound in the internal and external world that are received and decoded by receiver proteins called receptors, that are usually found embedded in the cell’s envelop, the plasma membrane. Upon receiving a signal, a receptor transmits the message to the inside of the cell, triggering specific cellular reactions.
GPCRs are a large family of receptor molecules with around 700 different types. In the current study, the researchers focus on a GPCR that serves as a receptor for the neuropeptide Y in cells and is called the Y2 receptor. Neuropeptide Y is a messenger hormone that primarily mediates signals between nerve cells, which is why Y2 receptors are mainly present in nerve cells.
Among other cellular reactions, the binding of neuropeptide Y to GPCR triggers the formation of new cell connections between neurons, or synapses. The local clustering of Y2 receptors on the surface of neurons is crucial for normal biological function (homeostasis) and neuronal plasticity.
Physiologically, Y2 receptor expression varies widely in different cells which makes receptor profiling on single cells a challenge. To address this challenge, and avoid artifacts in receptor clustering, the authors established a monoclonal human cervical cancer HeLa cell line expressing around 300,000 Y2 receptors per cell, and grew these cells on a specifically developed, light-sensitive matrix.
Each of the Y2 receptors was provided with a molecular “label.” Once the scientists directed a spot of light with a fine laser beam on the cell surface, the Y2 receptor under this spot were trapped via the molecular label to the exposed matrix in such a way that the Y2 receptors moved close together to form a cluster. The whole reaction could be immediately observed at the lighted spot within a few seconds.
“Within seconds, receptor clustering was modulated in size, location, and density,” the authors noted.
Following the light-induced entrapment and clustering of the receptors, the authors observed changes in cellular morphology, motility, and calcium signaling that revealed the receptors were activated in the absence of the ligand, neuropeptide Y.
This new method promises a novel approach to investigating mechanisms in cell signaling and the propagation of mechanical cues into biochemical signals.