Researchers discover unusual glassy behavior in an unhealthy protein

When UC Santa Barbara materials scientist Omar Saleh and student Ian Morgan sought to understand the mechanical behavior of unwritten proteins in the lab, they expected one particular model protein to return immediately, such as a rubber band.

Instead, this unwritten protein relaxed slowly, taking tens of minutes to relax into its original form – a behavior that resisted expectations, and hinted at an internal structure that had long been thought to exist but was difficult to prove.

“The rate of relaxation is important because it gives us some insight into the structural organization of the protein,” said Morgan, the lead author in a paper published in Physical assessment letters. “This is important because the structural organization of a protein is mostly related to its biological function.”

While a protein with solid ‘folds’ – a well-defined three-dimensional structure – is associated with its function, unorthodox proteins, with their unstable structures, derive their functions from their dynamics.

“More than 40% of human egg whites are at least partially excreted, and they are often linked to critical biological processes such as decaying diseases,” Morgan said.

The slow relaxation is actually a behavior that is typically reserved for filled egg whites.

“In the 1980s, it was discovered that folded proteins exhibited slow relaxations,” Morgan said, in a behavior typical of spectacles – a class of materials that are neither really liquid nor crystalline solids, but may exhibit characteristics of both state.

“We have been studying filled proteins for a long time and have developed many good tools for them, so it was soon found that the slow relaxations could be explained by a mechanism by which ‘frustrated’ molecules try themselves in a small space,” Morgan said. a mechanism called “jamming.” “This explanation helped us better understand the structure of folded egg whites and explain glass behavior in many other systems.”

The egg white, which the researchers tried to stretch through a device known as magnetic tweezers, was an inadvertent protein. By definition, it did not attempt to pack many molecules into a small space, so it would not have to run into problems, Saleh said.

“That, when we observed slow relaxations, it meant either our definition of the egg white was wrong or there had to be another mechanism,” Morgan said.

Furthermore, by relaxing the stretched protein but recalculating it with less force before it had a chance to fully relax, the researchers found that the protein “remembered” its previous stretching – initially extending, as expected with more force, but finally slowly relax again extend as expected with less force but then gradually relax over time. Conceptually, Morgan explained, the longer the egg white lasts, the longer it takes to relax, so it “reminds” him how long it was drawn.

To explain this unexpected, glassy behavior, the researchers drew inspiration from some rather mundane objects: crumpled paper and memory foam. Both structurally disturbed systems, they show a similar slow, logarithmic relaxation after being subjected to forces, and in particular in the case of the foam, a “memory” effect.

For the researchers, the behavior suggested that like memory foam and crumpled paper, the internal structure of the egg white was not one of one, solid unit, but one of several, independent substructures of a range of strengths between strong and weak that respond to a range of forces exerted on the material along different lengths of time. For example, strong structures can withstand a certain degree before they are pulled apart and be the first to relax, while weak structures with smaller forces stretch and take longer to relax.

Based on this understanding of multiple substructures and confirmed with experimental data, the researchers concluded that the logarithmic relational rate of the protein is inversely proportional to the stretching force.

“The stronger the stretching force applied to the unexplained protein, the more the protein relaxes at the same time,” Saleh explained.

“Mechanical misalignment systems with similar structural arrangements are often remarkably durable,” Morgan said. “They also have different mechanical properties, depending on how much you pull and compress them. This makes them very adaptable, depending on the size and frequency of the force.” Understanding the structure behind these adaptive skills could open the door to future dynamic materials, which, Morgan said, “just like your brain, help them filter out unimportant information and make it more efficient at storing repetitive stimuli.”