SerpApi.Org
Researchers at the University of Twente have developed an optical method that follows the shape changes of a single protein in liquid without attaching anything to it. It reads the protein's structure from its own molecular vibrations, free from the labels or tags that other techniques rely on. The method could help researchers study how proteins respond to drugs, toxins and other biomolecules. The paper is published in the journal ACS Nano.
Subscribe to our newsletter for the latest sci-tech news updates.
Proteins are often pictured as fixed 3D structures, one shape per molecule. In reality, they are restless. They bend, unfold, recover and switch between shapes while they carry drugs, bind other molecules and steer biological processes. Those motions are central to life, and they are very hard to observe directly, especially for one protein moving freely in liquid. Watching a single protein usually means pinning it down or attaching a marker, and either can change how it behaves.
Engineered metasurface
Every molecule vibrates in a characteristic way. Raman spectroscopy can detect those vibrations and reveal chemical and structural information. The signal from a single protein is normally far too weak to measure. The team solved this with a metasurface, a specially engineered surface of closely packed gold nanoparticles on a gold film.
When light hits the surface, it concentrates into tiny regions of intense electromagnetic field. A protein passing through one of these regions produces a Raman signal that is 10 million times brighter. From that signal, the researchers could read the protein's secondary structure and tell apart α-helices, β-sheets, β-turns and random-coil regions.
The protein needs no fluorescent label, chemical tag or mechanical tether, so its natural behavior stays intact. The team tested the method on bovine serum albumin, a common model for human serum albumin, the main transport protein in blood. Albumin carries fatty acids, hormones and many drugs.
Mapping the energy landscape
Because the measurements were made one protein at a time, the team could go beyond average structures. They constructed free-energy landscapes, which show which shapes a protein settles into most often and which are rarer but still within reach. They also mapped the routes between shapes. The main transitions ran between α-helix and β-sheet, and between α-helix and random coil.
"Our method gives access to the dynamic behavior of individual proteins in nearly physiological conditions," says Femi Ojambati, who led the work. "That matters, because we can learn more about a protein's function from the energy landscape, and also from the pathways between structures."
A tug-of-war over shape
The team then asked how the chemical environment steers a protein's shape. They added methyl, carboxylate and amine groups to the metasurface, groups that are common in biological and pharmaceutical molecules. They also varied the pH of the solution from acidic to neutral to basic. Electrostatic forces turned out to set the balance. At neutral pH, the native α-helical shape usually wins. Under other conditions, the protein leans toward β-sheet or random-coil shapes. Its surroundings, not just its sequence, decided which form it took.
Toward single-protein drug testing
The new technique might shed light on protein folding, misfolding and aggregation. Misfolding and aggregation play a role in diseases such as Alzheimer's, Parkinson's and type 2 diabetes. The researchers see the platform as a step toward label-free single-protein biophysics in realistic liquid environments. Better metasurface designs could capture even faster changes and extend the approach to larger biomolecules, including nucleic acids, carbohydrates and protein complexes.
More information: MohammadReza Aghdaee et al, Label-Free Single Protein Dynamics Revealed by Metasurface-Enhanced Raman Spectroscopy, ACS Nano (2026). DOI: 10.1021/acsnano.6c04055
Provided by University of Twente
This story was originally published on Phys.org.
