Scientists Bone-Up on Bones - the Oldest Protein Ever to be Sequenced
(Apr 24th 2007) Tyrannosaurus rex, a formidable and gruesome dinosaur, responsible for firing man's imagination ever since its discovery. A myriad of stories have evolved about this giant carnivore, most of them full of blood and gore. Scientists have recently added a new one, less terrifying but in no way less shocking. Annette Hupfer
When Mary Higby Schweitzer and her colleagues from North Carolina State University Raleigh unearthed one of the best preserved
Tyrannosaurus rex bones in Montana back in 2003, they committed something little short of sacrilege. They deliberately broke the colossal femur - one of the leg bones - because it would not fit into their helicopter! "How dare they!" you might exclaim and rightly so, it is indeed open to argument as to whether logistical problems are acceptable reasons for handling such an important palaeontological find in such a brutal way. However, without this certain inclination to "vandalism" the scientists would never have exposed the spectacular secret that the bones had been keeping safe inside. Soft tissues such as blood vessels were still present in the 68 million year old fossil! An unconceivable discovery as current fossilisation theories hold that after at least one million years, all traces of original organic material will have disappeared, completely replaced by minerals from the surrounding environment.
How the organic material has been preserved is still subject to wild speculation. There is no doubt that it is this kind of material; the latest findings, recently published in
Science, confirm this. Schweitzer's collaborator John Asara of Beth Israel Deaconess Medical Center and Harvard Medical School in Boston has even managed to decipher the collagen sequence extracted from those ancient bones, which now represents by far the oldest protein ever to have been sequenced.
"We looked for collagen because it's plentiful, durable and it's not something that any microbes living in the immediate environment could produce. So identifying collagen in the soft tissue would indicate that the tissue contains remnants of the molecules produced by the dinosaur, though highly altered," Schweitzer explained why they chose to look for exactly this protein. The palaeontologists first removed all minerals from the
Tyrannosaurus rex bone so that a fibrous matrix, which they suspected to be made of collagen, was left behind. Schweitzer and her colleagues inspected the tissue for collagen characteristics with both electron microscopy and atomic force microscopy. Then they tested it against various antibodies known to react with this protein. And finally, they sent a sample to Asara, a specialist in mass spectrometry. With his sophisticated version of this technique he was actually able to determine unique collagen sequences, thus providing the ultimate proof. By comparing the results with data from living animals they identified the
T. rex-collagen to be closest related to the chicken. That makes sense, after all, it is an established fact that birds and dinosaurs
are closely related.
The scientists now hope to have found a whole new way of studying evolution and finding evolutionary links between extinct and living species. Many colleagues are sceptical, however. It is very likely that extremely specific conditions are needed to preserve soft tissue over such vast periods of time. That given, the T. rex-collagen will probably remain a curiosity and an exceedingly intriguing one at that!
[1]
Science 316, p. 277-280
[2]
Science 316, p. 280-285
Photo: Mary Higby Schweitzer with a cast of a
Tyrannosaurus rex. (Photo from North Carolina State University).
