May 1, 2009

Paleontologists Sequence Dinosaur Proteins

A paleontologist at North Carolina State University says she has discovered new evidence to support the idea that soft tissue and proteins can be preserved over long periods of geological time after a protein sequence was recovered from an 80 million-year-old duck-billed hadrosaur.

Dr. Mary Schweitzer, along with colleagues Dr. John Asara of Beth Israel Deaconess Medical Center and Harvard Medical School, Dr. Chris Organ of Harvard Medical School, and a group of researchers from Montana State University examined the fossil remains of the Cretaceous Period dinosaur and published their results in Friday's edition of the nature journal Science.

In a previous research project, Schweitzer and Asara had utilized a number of modern lab techniques, such as mass spectroscopy, to analyze trace remnants of soft tissue recovered from a 68 million-year-old Tyrannosaurus Rex.  Their studies supported the controversial theory that these materials contained the remnants of original proteins from the extinct creatures.

In an effort to corroborate their previous research and to demonstrate that such preservation was not a unique event, the team began analyzing the significantly older hadrosaur remains, focusing their research around hypotheses regarding what types of environmental factors are likely to lead to the preservation of soft tissue.

Working with field crews from the Jack Horner's Museum, the team set out to find fossil remains that were preserved under particularly thick layers of sandstone. 

"Deep burial in sandstone seems to favor exceptional preservation," explained Schweitzer.  The particular fossil located in this dig was located beneath approximately seven meters of sandstone.

Using field techniques that aim to extract dinosaur remains without exposing them to the environment, they were able to extract a preserved femur from a Brachylophosaurus Canadensis "“ or hadrosaurus "“ found in the Judith River formation in Montana.

"This particular sample was chosen for study because it met our criteria for burial conditions of rapid burial in deep sandstones," said Schweitzer.

"We know the moment the fossil is removed from chemical equilibrium, any organic remains immediately become susceptible to degradation.  The more quickly we can get it from the ground to a test tube, the better chance we have of recovering original tissues and molecules."

Initial results seemed to indicate the success of their extraction methods and accuracy of their hypotheses. 

Images from both light and electron microscopes revealed images of a fibrous matrix and preserved microstructures typical of collagen and similar to those observed in the T. rex samples.

The group also tested the sample with antibodies that are known to react with collagen and other similar proteins.

Next, the samples were sent to a lab to be analyzed with a powerful, state-of-the-art mass spectrometer.  This device is common tool is a common tool in biochemical labs around the world and allows  scientists to look for specific peptide sequences "“ constitutive segments of proteins "“ that can then be weighed and compared with a library of known protein fragments of characteristic weights.

Mass spectroscopy analysis identified eight peptide segments from the hadrosaur that matched the characteristic weights for eight segments of collagen proteins.

These eight segments were then broken down and sequenced and compared against modern protein fragments from various lineages of animals.

According to Dr. Organ of Harvard Medical School, the sequence of the hadrosaur's collagen proteins more closely resembled proteins found in modern birds than those of alligators.

All results were independently checked by researchers at Montana State University, Harvard University, the Dana Farber Cancer Institute, and Matrix Science Ltd. of London.

Moreover, the group's results were consistent with the previous analysis of T. rex remains, indicating that the preservation of proteins may not be, as previously suggested, and entirely rare occurrence.

At the heart of the research project is the old question among paleontologists as to whether or not ancient proteins can be preserved at all.  When an animal dies, proteins are among the first biological macromolecules to begin decomposition.

This study, however, seems to indicate that under certain conditions proteins may indeed be preserved from decay "“ a revolutionary notion for a number of fields of study within the biological sciences.

"We wound up identifying nearly double the number of amino acids we recovered in the T. rex study," said Asara.  "The sequences displayed high spectral quality and the interpretations were of high confidence."

"We used improved methodology with better instrumentation, did more experiments and had the results verified by other independent labs," explained Schweitzer.  "These data not only build upon what we got from the T. rex, they take the research even further."

"I'm hoping in the future we can use this work as a jumping off point to look for other proteins that are more species-specific than collagen.  It will give us much clearer insight into all sorts of evolutionary questions."


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