In depth exploration of the hemolymph of Limulus polyphemus via combinatorial peptide ligand libraries

The hemolymph of Limulus polyphemus, a very ancient marine arthropod dating back to ca. 440 million years, has been explored in depth via capture by combinatorial peptide ligand libraries. Whereas barely a dozen proteins had been known up to the present, we have increased this number by more than 1 order of magnitude, up to 160 unique gene products, identified via the dbEST_limulus as well as via comparison with the other members of the Chelicerata subphylum to which Limulus belongs, namely, scorpions, ticks, mites, and spiders. Yet we have sequences of many other peptides, suggesting the presence of at least one more order of magnitude of species (1000 and more), that could not be identified as such sequences have no counterparts in present databases. This further reinforces the notion that these could be ancestral proteins, scarcely represented in present times. These data might represent the true birth of paleo-proteomics.