Water, Not Just Protein, May Drive Elastin's Spring-Like Recoil in Our Tissues

On November 9, a paper appeared in Nature Communications that takes up a question researchers have argued over for more than 50 years: what makes elastin spring back? Elastin is the protein that lets arteries swell and recoil with each heartbeat, lets lungs stretch and relax as we breathe, and gives skin some of its ability to return to shape.

The authors are Anna Tarakanova, an associate professor in the School of Mechanical, Aerospace, and Manufacturing Engineering at the University of Connecticut College of Engineering, and postdoctoral researcher Metehan Çam. Their evidence points to water as playing a much larger part than had been understood. "Elastin is the body's natural spring," Tarakanova said.

Two older explanations have long competed. One compares elastin to a rubber band: stretching restricts the protein's molecular movements, and the protein tends to recoil toward a freer state. The other puts the emphasis on the water molecules surrounding the protein. Both rest on entropy, the idea that describes how many different ways molecules can move and arrange themselves.

Tarakanova and Çam found that stretching elastin exposes more of its surface to water. Additional water molecules are drawn into a thin layer around the protein, where they have less freedom of movement than water farther away. When the protein relaxes, some of those molecules return to the surrounding liquid and regain that freedom. "The protein's flexibility still matters, but hydration water makes the dominant contribution to the entropy changes we measured," Çam said. Tarakanova put the broader picture this way: elastin should be viewed as a coupled protein-water system, not simply a dry molecular spring.

The work builds on earlier evidence for a water-driven mechanism, while showing that both protein flexibility and water interactions contribute.

The method matters here. The team built an atom-by-atom computer model of a 225-amino-acid region of human tropoelastin, the molecular building block of elastin. They ran it on the Anton 3 supercomputer at the Pittsburgh Supercomputing Center, made available by D.E. Shaw Research. The simulation tracked the protein's relaxed state for 60 microseconds and compared it with a fully extended reference state. Earlier studies generally measured the combined effect of protein and water together. This approach let the researchers calculate the entropy of each component separately, and observe molecular motions that are hard to capture experimentally.

The findings may bear on aging. As people get older, elastin fibers can undergo chemical modifications, and tissues such as arteries, skin, and lungs gradually lose some elasticity. "Our results suggest that we should examine not only changes in elastin's structure, but also how those changes affect its interactions with water," Tarakanova said. Future studies could test whether age-related chemical changes alter the water layer around elastin, which might shed light on tissue stiffness and declining resilience. The results could also inform elastin-inspired biomaterials designed to withstand repeated stretching, with possible uses in tissue engineering.

Next, the team plans to extend its models to more complex systems, including multiple protein chains and the interconnected elastic fiber networks found in human tissues. "Ultimately we hope to connect these molecular mechanisms with the mechanical behavior of tissues and engineered materials," said Çam.