Imma Perfetto
Cosmos science journalist
Fragments of the protein collagen have been found preserved in dinosaur fossils 80 million to195 million years old.
But this shouldn’t be possible. With a half-life of only about 500 years, the peptide bonds that hold proteins together ought to break down much, much sooner.
Now, a new study in ACS Central Science has described the protective chemistry responsible for collagen’s extraordinary longevity.
As the most abundant protein in animals, collagen can be found in the bones, skin, muscles and ligaments.
Senior author of the study, Ron Raines, a professor of chemistry at Massachusetts Institute of Technology (MIT) in the US, says collagen is the scaffold that holds us together.
“What makes the collagen protein so stable, and such a good choice for this scaffold, is that, unlike most proteins, it’s fibrous,” says Raines.
It’s made up of long strands of amino acids that intertwine like rope to form a triple helix structure. It’s this structure that gives collagen’s peptide bonds their unique resistance to breakdown by water (hydrolysis).
The peptide bonds linking consecutive amino acids in a protein are formed between a carbon atom in the one amino acid and a nitrogen atom in the adjacent amino acid.
The carbon atom also forms a double bond with an oxygen atom, forming a molecular structure known as a carbonyl group.
This carbonyl oxygen has a pair of electrons that don’t form bonds with any other atoms. Those electrons, the researchers found, can be shared with the carbonyl group of a neighbouring peptide bond.
Because these interactions engage virtually every peptide bond in the collagen triple helix, it staves off water molecules that would ordinarily make their way into the structure to disrupt those bonds through hydrolysis.
“Collagen is all triple helices, from one end to the other,” Raines says.
“There’s no weak link, and that’s why I think it has survived.”
The researchers say that the lessons learned from these interactions can guide the design of other exceptionally stable, long-lived materials.
