Protein sequences bound to mineral surfaces persist into deep time

Beatrice Demarchi, Shaun Hall, Teresa Roncal-Herrero, Colin L Freeman, Jos Woolley, Molly K Crisp, Julie Wilson, Anna Fotakis, Roman Fischer, Benedikt M Kessler, Rosa Rakownikow Jersie-Christensen, Jesper V Olsen, James Haile, Jessica Thomas, Curtis W Marean, John Parkington, Samantha Presslee, Julia Lee-Thorp, Peter Ditchfield, Jacqueline F Hamilton, Martyn W Ward, Chunting Michelle Wang, Marvin D Shaw, Terry Harrison, Manuel Domínguez-Rodrigo, Ross DE MacPhee, Amandus Kwekason, Michaela Ecker, Liora Kolska Horwitz, Michael Chazan, Roland Kröger, Jane Thomas-Oates, John H Harding, Enrico Cappellini, Kirsty Penkman, Matthew J Collins

Proteins persist longer in the fossil record than DNA, but the longevity, survival mechanisms and substrates remain contested. Here, we demonstrate the role of mineral binding in preserving the protein sequence in ostrich (Struthionidae) eggshell, including from the palaeontological sites of Laetoli (3.8 Ma) and Olduvai Gorge (1.3 Ma) in Tanzania. By tracking protein diagenesis back in time we find consistent patterns of preservation, demonstrating authenticity of the surviving sequences. Molecular dynamics simulations of struthiocalcin-1 and -2, the dominant proteins within the eggshell, reveal that distinct domains bind to the mineral surface. It is the domain with the strongest calculated binding energy to the calcite surface that is selectively preserved. Thermal age calculations demonstrate that the Laetoli and Olduvai peptides are 50 times older than any previously authenticated sequence (equivalent to ~16 Ma at a constant 10°C).