Receptor ‘Energy Maps’ Chart New Territory for Drug Discovery

The National Institute of Neurological Disorders and Stroke awarded him an additional $530,000 for the project “Multiple Activity Patterns of Acetylcholine Receptors” — now in its 26th year of funding. In addition, he will receive $2.4 million to continue the project, “Engineering a Transmitter Binding Site,” for five years.

Using the nerve-muscle synaptic receptor as a model system, Auerbach and his team are working to measure the energy changes associated with each moving part of the acetylcholine receptor (AChR), piece by piece.

Acetylcholine — a common neurotransmitter — is a chemical compound released by nerves that activates muscles, among other functions. The chemical’s receptor is an ion channel membrane protein that “gates” the flow of ions at the nerve-muscle synapse.

“We invented new ways to make maps of the energy changes inside the protein and pinpoint what parts are most important for the receptor’s activation,” Auerbach explains. “As far as I know, ours is the only lab currently making such energy maps.”

“By doing so, we will understand, design and control how this receptor responds to drugs,” he says. “The knowledge gained will be applied to a broad class of receptors important in human health and disease,” including those that play roles in behavior and diseases of the nervous system, he says.

The maps are revealing the microscopic events that occur when neurotransmitter molecules released from a nerve terminal bind to AChRs.

“We probe in detail how the chemical binds to the protein receptor and how the protein actually switches between resting (closed) and active (open) shapes during the gating process,” Auerbach notes.

Auerbach is focusing on the gating mechanisms that cause the neuromuscular acetylcholine receptor to open or close at the neurotransmitter binding sites. Gating is necessary for the transmission of chemical signals from nerves to muscles.

In its open configuration, the receptor allows ions to pass through; when closed, ion permeation is forbidden.

His team has already delineated four steps by which these receptors change from closed to open.

“We will now use single-channel kinetics and phi-value analysis to probe the interior of AChR gating and illuminate the ultra-fast protein rearrangements within this reaction,” he says.

The researchers will test two new hypotheses; they will explore how the binding sites and the gate communicate, and they will study the role of spontaneous activity of receptors in cellular communication processes.

Auerbach and his team also are working to establish fundamental principles for engineering a protein to respond in predictable ways to specific drugs.

Drug action depends on the differential binding of ligands, or binding molecules, to inactive (closed) versus active (open) conformations of a receptor. “To address this, we will study gating and energy flow inside the protein in the absence of ligands using single-channel electrophysiology and kinetic analysis,” Auerbach says.

The principles learned can help researchers understand the biophysical mechanisms of ligand-protein complexes such as neurotransmitters, and hence, the mechanisms by which a drug causes a protein to change shape.

“Eventually, the knowledge gained will be used to engineer acetylcholine receptors that respond predictably to arbitrary ligands — versatile molecules that bind to diverse targets,” he notes.

“This knowledge also will advance our ability to design new drugs targeting various types of receptors.”

Auerbach hopes to continue shedding light on cellular communication that occurs via complex chemical signaling, a process needed for physiological functions.

“Because many diseases and most drugs modify or interrupt chemical signaling, this work will create powerful tools for designing new drugs and controlling cellular responses,” Auerbach notes.

In addition, the knowledge gained “will enable us to engineer the properties of receptors in living systems,” also facilitating new disease treatments, Auerbach adds.

“Like all basic research, this will take time,” he acknowledges, “so we must be patient.”

“This type of research extends the horizon for inventing new therapies — it can have future payoffs for medicine that cannot be predicted,” he emphasizes.

His research combines multifaceted approaches, including pharmacology, enzymology, structural and molecular biology, electrophysiology and mathematical modeling.