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posted 18. April 2003 13:18
Chemical & Engineering News on April 16
http://pubs.acs.org/cen/today/april16.html
ANCIENT PROTEINS REVEAL THE PAST
Mass spectroscopic amino acid sequencing methods open genetic window to long ago
[ISCID Editor's Note: Exerpts of article provided below. For the full article, please visit the link above]
AMANDA YARNELL, C&EN WASHINGTON
After years of relying solely on DNA sequencing, geochemists have finally developed methods for sequencing ancient proteins that may make the retrieval of genetic information from creatures that lived hundreds of thousands of years ago a realistic possibility. The advance will allow scientists to more reliably reconstruct phylogenic relationships between ancient organisms and their modern counterparts.
Attempts to sequence DNA from fossils--some more successful than others--have been going on for more than a decade. Trace amounts of DNA can be extracted from fossils, amplified to a detectable signal using the polymerase chain reaction, and then sequenced. Sequencing of ancient DNA has been a boon to scientists hoping to track the evolution of modern humans, trace the migrations of animal populations over time, and determine the geographic origins of fossilized plants and animals.
But the fragility of DNA--its phosphate backbone is easily hydrolyzed and enzymes that degrade it are hard to get rid of--makes sequencing of DNA from very old samples extremely difficult. As a consequence, the study of ancient DNA sequences is likely to be limited to those from fossils less than 100,000 years old and perhaps much younger. In addition, the technical difficulty of distinguishing sample DNA from that of common contaminants such as fungi and bacteria calls into question the reliability of ancient DNA analysis.
Scientists have long suspected that some proteins might outlast DNA in very old samples. Theoretical calculations suggest that proteins may survive for more than a half a million years at ambient temperatures [The Biochemist, 24, 12 (2002)]. Ancient protein sequencing has proved difficult, however, leaving ancient DNA sequencing the only game in town.
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Ancient protein sequencing will unlock a "treasure of untapped genetic information," Ostrom told C&EN. But, she acknowledged, the genetic information content of protein sequences is not as rich as that gleaned from DNA. She and Nielsen-Marsh hope that their search for other well-preserved proteins will turn up ones boasting greater amino-acid sequence variability--a feature that would yield more information for reconstructing phylogenic relationships.
"Protein sequences may not change as rapidly as DNA sequences," Nielsen-Marsh said, "but because proteins are inherently more stable, they offer a unique opportunity to extend the search for biomolecules further back in time." That makes it possible that ancient protein sequencing might be archaeologists' and paleobiologists' most dangerous weapon yet.
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