Chemists explain why dinosaur collagen was able to survive for millions of years

Collagen, a protein found in bones and connective tissues, has been found in dinosaur fossils that are 195 million years old. This lifespan is much longer than the normal half-life of the peptide bonds that hold proteins together, which is about 500 years.

A new study from MIT explains why collagen can survive much longer than expected. The research team discovered that a special interaction at the atomic level protects collagen from attack by water molecules. This barrier prevents water from breaking the peptide bonds through a process called hydrolysis.

“We provide evidence that this interaction prevents water from attacking peptide bonds and cleaving them. This is in contrast to what happens with a normal peptide bond, which has a half-life of only 500 years,” says Ron Raines, Firmenich Professor of Chemistry at MIT.

Raines is the lead author of the new study, which appears Central Scientific Center of the ACSJinyi Yang, Ph.D., a postdoctoral fellow at MIT, is the lead author of the study. Volga Kojasoy, a postdoctoral fellow at MIT, and Gerard Porter, a graduate student, are also authors of the study.

Water resistant

Collagen is the most abundant protein in animals. It is found not only in bones, but also in skin, muscles, and ligaments. It is made up of long strands of protein that intertwine to form a tough triple helix.

“Collagen is the scaffolding that holds us together,” Raines says. “What makes collagen protein so stable and such a good choice for that scaffolding is that unlike most proteins, it’s fibrous.”

Over the past decade, paleobiologists have found evidence of preserved collagen in dinosaur fossils, including an 80-million-year-old Tyrannosaurus rex fossil and a nearly 200-million-year-old sauropodomorph fossil.

For 25 years, Raines’ lab has been studying collagen and how its structure enables its function. In the new study, they reveal why the peptide bonds that hold collagen together are so resistant to degradation by water.

Peptide bonds are formed between a carbon atom of one amino acid and a nitrogen atom of the adjacent amino acid. The carbon atom also forms a double bond with an oxygen atom, forming a molecular structure called a carbonyl group. This carbonyl oxygen has a pair of electrons that do not bond with any other atom. Researchers have discovered that these electrons can be shared with the carbonyl group of a neighboring peptide bond.

Because this electron pair is inserted into these peptide bonds, water molecules cannot enter the structure to disrupt the bond.

To demonstrate this, Raines and his colleagues created two interconverting mimics of collagen: one that typically forms a triple helix, called trans, and one in which the angles of the peptide bonds are rotated to a different form, called cis. They found that the trans form of collagen did not allow water to attack and hydrolyze the bond. In the cis form, water got in and the bonds were broken.

“A peptide bond is either cis or trans, and we can change the cis/trans ratio. By doing this, we can mimic the natural state of collagen or create an unprotected peptide bond. And we found that when it was unprotected, it wasn’t available for long,” Raines says.

“No weak link”

This electron sharing has also been observed in protein structures called alpha helices, which are found in many proteins. These helices can also be protected from water, but they are still connected by more exposed protein sequences, which are still susceptible to hydrolysis.

“Collagen is made up of three helices, end to end,” Raines says. “There are no weak links, and that’s why I think it survived.”

Previously, some scientists have suggested other explanations for why collagen might be preserved for millions of years, including the possibility that the bones were so dehydrated that no water could reach the peptide bonds.

“I can’t rule out other factors, but 200 million years is a long time, and I think it takes something at the molecular level, at the atomic level, to explain it,” Raines says.

This article is republished with kind permission from MIT News (web.mit.edu/newsoffice/), a popular site covering the latest research, innovation, and teaching at MIT.