2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
American researchers have discovered the mechanism of green fluorescence in feline sharks. It turned out that the role of absorber-emitters is not high-molecular proteins, as in most other fluorescent organisms, but small molecules from a previously undescribed family of bromo-kinurinins, and scales on shark skin act as light guides. In addition, new representatives of kinuridines have antibacterial properties, the authors write in an article in iScience (a new magazine from CellPress).
Luminous living organisms are widespread in nature. Their luminescence can be caused both by bioluminescence (which, for example, mushrooms glowing in the dark possess), which does not require an external light source, or biofluorescence, which consists in the reverse emission of absorbed light with a changed wavelength. As a rule, marine organisms are capable of biofluorescence, the most studied of which are jellyfish and corals, in which special proteins play the role of fluorophores. The Nobel Prize in Chemistry was awarded in 2008 for the discovery of the green fluorescent protein (GFP - green fluorescent protein) of the jellyfish Aequorea victoria. Green protein and its derivatives are currently widely used in biological experiments for labeling cellular components.
In 2014, the team of David Gruber of the American Museum of Natural History (New York) showed that a large number of marine fish species also have the ability to biofluorescence. For only a few of them, the mechanism underlying this phenomenon has been described - for example, the fatty acid binding protein (FABP) was responsible for the fluorescence of the Japanese eel.
In a new work, Gruber and Jason Crawford from the Yale University Department of Chemistry (USA) described the biofluorescence mechanism of the skin of two shark species, which turned out to be different from all known before. Shark biofluorescence turned out to be caused not by proteins, but by small molecules - products of tryptophan metabolism.
Fluorescence of a section of the skin of a shark Cephaloscyllium ventriosum, irradiated with blue light
The objects of research of scientists were the California cat-head shark Cephaloscyllium ventriosum, which inhabits the Pacific Ocean basin, and the reticulated cat shark Scyliorhinus retifer from the western Atlantic. Earlier, Gruber's team found that in the blue light that prevails in the depths of shark habitat, the skin of these fish glows bright green. Using a range of spectrometric methods, such as high-resolution mass spectrometry and UV spectroscopy, scientists have identified in shark skin a previously undescribed family of small fluorescent molecules - bromine-containing kynurenines.
In mammals, kynurenine derivatives are found in the nervous system and, apparently, play the role of signaling molecules. However, the synthesis of these molecules in sharks, most likely, occurs along an alternative pathway, different from mammals, and performs different functions. It is possible that bromo-kynurenines play the role of UV filters, interacting with melanin in shark skin. In addition, given the monochromatic vision of sharks, fluorescence itself is likely to play a role in intraspecific interactions in fish.
New molecules from the kynurenine class that function as fluorophores in shark skin
Since cat sharks live on the bottom, scientists have suggested that bromine-kynurenines may also protect their skin from bottom bacteria. Indeed, in a preliminary experiment, these substances were able to inhibit the growth of both the common marine bacterium Vibrio parahaemolyticus and methicillin-resistant Staphylococcus aureus.