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Ancient eggshell protein breaks DNA time barrier

Posted on 27 September 2016

An international study involving researchers in the Chemistry department at York have unlocked a key to obtaining ancient protein sequences much older than was previously thought possible, thanks to the help of ancient ostrich eggshells.

Scientists have identified fossil proteins in ostrich eggshells

An interdisciplinary study, published in the journal ELife, suggests that analysis of ancient fossil proteins in a 3.8 million year-old ostrich eggshell could provide genetic information almost 50 times older than previously thought. Crucially, the findings provide archaeologists and palaeontologists with the ability to be more targeted in which fossils they select for deeper analysis.

Ostrich eggshells are a common find at fossil sites in Africa and are packed full of proteins which regulate the shell’s growth. With the expertise of the Chemistry department (NEaar lab, Centre of Excellence in Mass Spectrometry and Wolfson Atmospheric Chemistry Laboratories) and using state of the art proteomics (by mass spectrometry), chiral amino acids and volatile organic compound analysis, the York researchers tracked older and older fossils from very well-dated sites in Tanzania and South Africa, spanning the last 3.8 million years.

Dr Beatrice Demarchi, from the University of York’s Department of Archaeology, said: “Evidence suggested that it was the more fluid, unstable, region of the protein that promoted and regulated mineral growth in the shell, but it was also less likely to survive over time and the intense heat of the African climate.” However as the York team examined older and older eggshells, it was the more unstable regions which survived the best.

Dr Kirsty Penkman, who led the chiral amino acid and volatile organics work at York, said: “The remarkable thing is that for the first time we can prove that these fossil sequences are authentic, because of the overwhelming combination of multiple lines of evidence.”

Professor Matthew Collins, from the University of York’s Department of Archaeology, said: "To date, DNA analysis from frozen sediments has been able to reach back to about 700,000 years ago, but human evolution left most of its traces in Africa and the higher temperature there takes its toll on DNA preservation. We had known for many years that proteins could give more clues into the past, but when we looked at protein decay in eggshells, it gave us unusual results when compared to other fossil materials and, until now, we have not really known why.”

In collaboration with computational materials scientists, simulations showed the regions that should be chemically unstable were the strongest binders to the mineral. Only one peptide sequence survived consistently in samples dated beyond 1 million years, the same one identified theoretically by the Sheffield team. Remarkably, in the oldest eggshell in the study - from the famous Australopithecus footprints site of Laetoli in Tanzania (3.8 million years) - the peptide was still there.

To read the full story, visit http://www.york.ac.uk/news-and-events/news/2016/research/ancient-protein-osterich-egg-shell/ or http://www.bbc.co.uk/news/science-environment-37473388.

Notes to editors:

  • The paper, Protein sequences bound to mineral surfaces persist into deep time,is published here: https://elifesciences.org/content/5/e17092/figure4
  • The work in Chemistry was funded with the support of NERC and the Leverhulme Trust
  • This collaborative study included researchers from the University of Sheffield, University of Copenhagen, University of Oxford, Bangor University, Arizona State University, Nelson Mandela Metropolitan University, University of Cape Town, New York University, Complutense University of Madrid, American Museum of Natural History, National Museum of Tanzania, The Hebrew University, University of Toronto, and the University of the Witwatersrand
  • For more information about the Department of Archaeology, visit http://www.york.ac.uk/archaeology/