Siberian Federal University: From blue to red: scientists experiment with the “living light” of jellyfish

Scientists of Siberian Federal University in collaboration with colleagues from the Institute of Biophysics of the Federal Research Center, Krasnoyarsk Scientific Center, SB RAS and researchers from ShanghaiTech University (China) studied the photoprotein obelin, which can be used to create bioluminescent test systems. Since photoproteins, in particular, obelin, can emit bright light when calcium ions are added, they are actively used as intracellular markers for monitoring various cellular processes. Also, obelin can be used in test systems for enzyme immunoassay, which allows you to diagnose various diseases caused by bacterial cells, viruses, fungi, protozoa and parasites. The study considers obelin activated not by a natural substrate, but by its synthetic analogue.

Photoproteins are bioluminescent proteins capable of emitting light during a chemical reaction. The substrate necessary for the bioluminescent reaction of photoproteins to occur is a special molecule, coelenterazine. In nature, photoproteins are found in many marine organisms, such as luminous marine hydroid polyps. These inhabitants of seas and, more rarely, freshwater form large colonies and lead a predatory lifestyle.

To date, an urgent task is to change the properties of photoproteins in order to expand the range of their application. For example, it is well known that the tissues of living organisms poorly transmit blue light and transmit red well. Therefore, in order to effectively use photoproteins to visualize internal processes in tissues, it is better to make their luminescence shift to the red region of the spectrum. However, natural photoproteins glow blue. It is possible to chemically modify the substrate molecule in such a way that the resulting glow of the protein turns yellow or red. Coelenterazine-v will help in this. It is a well-known chemical analogue of the natural substrate of photoprotein bioluminescence — coelenterazine. Coelenterazine-v is just able to change the color of the radiation to a redder one. However, photoproteins activated by this analog glow very weakly, with low efficiency, which significantly reduces their practical potential. A group of scientists, which included SibFU experts, found out the reasons for the low efficiency of photoproteins with coelenterazine-v.

“Using the methods of crystallography and X-ray diffraction analysis, our scientific team, together with colleagues from China, managed to solve the three-dimensional spatial structure of obelin activated with coelenterazine-v (obelin-v)”, said Elena Eremeeva, co-author of the study, associate professor of the Department of Biophysics and the Basic Department of Biotechnology of SibFU, senior researcher of the Institute of Biophysics of the Federal Research Center, Krasnoyarsk Scientific Center, SB RAS. “This made it possible to see how and in what form the new substrate is integrated into the active center of the protein, and to make sure that the structure of the protein is not disturbed”.

According to the researcher, the comparison of the structure of obelin-v with that of obelin activated with conventional coelenterazine revealed important differences between the two protein variants that may underlie the low efficiency of obelin-v bioluminescence. The study also describes in detail the bioluminescent and fluorescent properties of obelin-v and considers their relationship with the structural organization of the protein.

The scientists reported that the next stage of their work would be to obtain a different spatial structure – obelin-v after a bioluminescent reaction. By comparing all available structures with each other, before and after the reaction, with natural and chemically modified substrates, scientists hope to identify the reasons for the low bioluminescent activity of photoproteins with coelenterazine-v and to correct this shortcoming in the future. Then photoproteins can be used as a sensor for visualizing processes in tissues with much greater efficiency.

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