Bromotryptophan is a noncoded amino acid that is rarely found in peptides formed in the cell's ribosome. It is a product of post-translational modification. Bromotryptophan and its analogs seldom occur in peptides that are not produced through the ribosomal machinery.
Elsie C. Jimenez, a researcher from the University of the Philippines Baguio has studied marine bromopeptides in detail and published a review in Protein and Peptide Letters. Jimenez notes that, of the characterized peptides, the ribosomal peptides generally contain 6- bromo-L-tryptophan. Non-ribosomal peptides have brominated tryptophan analogs and unusual peptidic structures.
Peptide molecules are susceptible to proteolytic degradation, but the presence of brominated tryptophan analogs may provide structural stability that could prevent degradation due to the steric effect caused by the bromine atom. Brominated tryptophan analogs likely have important functions in the lives of marine animals, such as cone snails, ascidians, hagfish, annelids, sea urchins and sponges. The peptides containing brominated tryptophan analogs show important biological activities that the animals can use for chemical defenses. "Several peptides reveal pharmacological activities that can be further explored for medical applications", says Jimenez.
"Some peptides cause excitatory activities while others bind to nervous system receptors. The rest show antimicrobial, insecticidal, hemolytic and cytotoxic activities." The presence of brominated tryptophan analogs possibly makes these peptides ideally fit to target cell membranes. Peptides that show antimicrobial activities may be developed as antibiotics. Those that bind to specific receptors may be tapped for treatment of neurological disorders. Peptides with antitumor activity may be developed as cancer drugs.
So far, no brominated tryptophan-containing peptide from marine animal has been approved for therapeutic use. However, the distinct characteristics of these peptides are thought-provoking for further studies, including the investigation of their biosynthesis and mechanisms of action.