Molecular Phylogeny of "Chemosensory Proteins" in Bacteria and Arthropods: CSP as an Extremely Ancient Gene

In this research paper, I provided a comprehensive overview of "Chemosensory Proteins" (CSPs), which have traditionally been thought to be involved in transporting odorant or tastant molecules to chemosensory receptors. However, CSPs are perplexingly expressed in various other organs and likely serve purposes other than chemosensing. By searching against microbial and crustacean protein databases, I found that CSPs are present not only in insects and other arthropods but also in bacteria. Given that CSPs are present from prokaryotes to insects and arthropods, and are expressed in many various tissues, I came to the conclusion that CSPs are unlikely to have purely chemosensory functions. This is consistent with most recent findings in the chemosensory field of Drosophila, where CSPs and odorant-binding proteins are thought to have functions beyond acting as odorant/tastant binding molecules.