28 September 2016
Ancient eggshell protein breaks through the DNA time barrier
Researchers from Centre for GeoGenetics, the University of York, and the University of Sheffield have unlocked a key to obtaining ancient protein sequences much older than was previously thought thanks to the help of ancient ostrich eggshells.
Research, 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 with the ability to be more targeted in which fossils they select for deeper analysis.
Research, published in the journal ELife suggests the survival of these ancient protein fragments could shed new light on how animals and humans lived and interacted in the past, how some species became extinct, and why some evolved and continue to thrive today. Crucially, the findings provide archaeologists with the ability to be more targeted in which fossils they select for deeper analysis.
The University teams analysed and tracked progressively older egg fossils from well-dated sites in Tanzania and South Africa, where it is expected DNA and proteins would not survive the extreme environmental conditions.
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.
Scientists had known for many years that proteins could give more clues into the past, but when they looked at protein decay in eggshells, it gave them unexpected results when compared to other fossil materials and, until now, they have not really known why.
Fragments of ostrich eggshells are abundant in Africa, and often found at archaeological and palaeontological sites as they were exploited by the earliest modern humans as raw materials to make art, and jewellery or for carrying water. The shell is very thick and hard wearing and because it survives under many different environmental conditions it is a good material to study.
The researchers speculated that proteins might survive better if they were stuck onto solid surfaces, and so they tested the theory with the support of computational scientists at the University of Sheffield, who modelled the bindings of proteins in ostrich eggshells.
Dr Beatrice Demarchi, from the University of York’s Department of Archaeology and lead author of the article, said :
Evidence suggested that it was the more flexible, 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.
As the researchers examined older and older eggshells, they could see that this assumption was surprisingly wrong, as it was in fact the unstable regions that survived the best. They were able to bind more strongly to the eggshell, allowing it be preserved in time.
The remarkable thing is that for the first time the scientists can prove that these fossil sequences are authentic, because of the overwhelming combination of multiple lines of evidence. Dr Enrico Cappellini, from Centre for GeoGenetics at University of Copenhagen said:
Excitingly, from the oldest eggshell in the study – from the 3.8 million year-old site of Laetoli in Tanzania – this region of the protein was still preserved, giving us a unique insight into what to look for when analysing fossils of this kind. Now that we know minerals can trap and preserve proteins in this way, we can be much more targeted in our study of ancient remains.
The research is published in the journal ELife http://dx.doi.org/10.7554/eLife.17092.018 and included a researchers from Universities in the Europe, the USA and Africa