Surveying the sequence diversity of model prebiotic peptides by mass spectrometry

The rise of peptides with secondary structures and functions would have been a key step in the chemical evolution which led to life. As with modern biology, amino acid sequence would have been a primary determinant of peptide structure and activity in an origins-of-life scenario. It is a commonly held hypothesis that unique functional sequences would have emerged from a diverse soup of proto-peptides, yet there is a lack of experimental data in support of this. Whereas the majority of studies in the field focus on peptides containing only one or two types of amino acids, here we used modern mass spectrometry (MS)-based techniques to separate and sequence de novo proto-peptides containing broader combinations of prebiotically plausible monomers. Using a dry-wet environmental cycling protocol, hundreds of proto-peptide sequences were formed over a mere 4 d of reaction. Sequence homology diagrams were constructed to compare experimental and theoretical sequence spaces of tetrameric proto-peptides. MS-based analyses such as this will be increasingly necessary as origins-of-life researchers move toward systems-level investigations of prebiotic chemistry.