Published online 14 June 2011 | Nature | doi:10.1038/news.2011.369

News

Collagen coils might have kept Tyrannosaurus molecules safe from harm for millions of years.

Researchers are divided on whether Tyrannosaurus rex proteins have survived to the present day. L. Psihoyos/Corbis

Scientists have discovered how fragments of the protein collagen might have survived in fossilized dinosaur bones. The intertwining, rope-like structure of the molecule, a major component of bone, could have shielded parts of the protein from enzymes and the elements for tens of millions of years, they say.

The results, which are published in PLoS ONE1, support the contentious claim that dinosaur proteins have been recovered and sequenced.

Collagen molecules consist of three long protein subunits that coil around each other in a triple helix. Five of these helices wind together to make up a microfibril, and thousands of microfibrils gather to form a fibril.

"It's like a massive, multi-stranded rope," says James San Antonio, lead author of the paper and a biochemist at Orthovita, a medical-implant manufacturer in Malvern, Philadelphia.

San Antonio and his colleagues analysed 11 fragments of collagen recovered from the fossilized bones of a 68-million-year-old Tyrannosaurus rex and an 80-million-year-old Brachylophosaurus canadensis.

Mary Schweitzer, a palaeontologist at North Carolina State University in Raleigh, and her colleagues have previously claimed to have found soft tissues and collagen in these remains2,3. Other scientists think that the recovered proteins are modern contaminants (see 'Origin of T. rex protein questioned')

Protein puzzle

San Antonio's team compared the recovered collagen fragments with models of human and rat collagen, and found that all 11 pieces came from the innermost parts of the microfibrils. Some originated in the same location in both dinosaurs. The researchers say that sites deep inside the collagen fibre would have been shielded from degrading enzymes and the environment.

The recovered collagen also contains very few acidic amino acids, constituents of protein that are particularly vulnerable to degradation by enzymes and water. Joseph Orgel, a co-author of the report who studies collagen at the Illinois Institute of Technology in Chicago, adds that collagen fibres are often buried within bone, which could preserve them "far beyond our current best estimates".

The study is "interesting and plausible, but speculative", says Marshall Bern, a computer scientist at Palo Alto Research Center in California, who has also analysed dinosaur-protein data. "It's hard to extrapolate too far from the little bit of sequence that has been found," he says.

Others are more sceptical. Stephen Salzberg, a geneticist at the University of Maryland in College Park, has already posted a critical comment about the paper at PLoS ONE, saying that the peptides that the team analysed "are contaminants from modern species".

Bone of contention

Salzberg says that the oldest verified proteins are bacterial molecules hundreds of thousands of years old found in ice cores. The dinosaur bones are many times older than that, and were found in temperate Idaho. Theoretical predictions and lab experiments suggest that proteins cannot survive for more than a few million years.

But Schweitzer, who also contributed to the latest study, counters that if the collagen fragments were contaminants, they should have come from random parts of the structure. Instead, they all came from the most protected parts of the microfibril, supporting the idea that they are genuine dinosaur relics.

ADVERTISEMENT

Schweitzer notes that her claims have been supported by two labs besides her own3. Furthermore, no collagen was found in sediments around the fossils, as would have been expected if the molecules were contaminants; and the team got positive results when testing the samples using antibodies that stick to collagen and other bone proteins.

As well as telling us how dinosaurs lived, Schweitzer believes that work on their proteins could inform the design of more effective and resilient collagen for use in prostheses or medical implants.

"The first and largest hurdle has been to convince people that this stuff is real," she says. "This paper is a step in that direction."