Comparison of the Size and Properties of the Cytochrome c/Cardiolipin Nanospheres in a Sediment and Non-polar Medium
Apoptosis, as the major type of programmed cell death, plays an important role in the organism renewal and removal of defective and transformed cells, including cancer cells. One of the earliest apoptotic events is lipid peroxidation in the inner mitochondrial membrane catalyzed by a complex of cytochrome c (CytC) with the mitochondrial phospholipid cardiolipin (CL). It was shown that mixing CytC and CL solutions results in the formation of CytC/CL complexes (Cyt-CL nanospheres) with a diameter of 11–12 nm composed of the molten globule protein molecule and a CL monolayer. Using the methods of dynamic light scattering for the Cyt-CL chloroform solution and small-angle X-ray scattering for the Cyt-CL sediment, it was found that in both cases, Cyt-CL formed nanospheres with a diameter of 8 and 11 nm, which corresponded to the earlier determined lipid/protein ratios of 13–14 and 35–50, respectively. These results showed that the Cyt-CL nanospheres can form not only during crystallization but also in a hydrophobic medium. CytC in the complex exists as a molten globule, as evidenced by the emergence of tryptophan and tyrosine fluorescence (absent in the native protein) due to the Förster resonance transfer of the electron excitation energy onto the heme. At the same time, the coordinate bond between the heme iron and the sulfur atom of methionine 80 in Cyt-CL is disrupted (the absorption band at ~700 nm disappears). Similar disruption of the iron-sulfur bond in Cyt-CL was observed in 50% methanol. These changes were reversible, which corroborates the conclusion on the CytC transition to the molten globule conformation in methanol-containing solutions.
Keywordsapoptosis cytochrome c cardiolipin Cyt-CL complex hydrophobic medium dynamic light scattering small-angle X-ray scattering molten globule
iron-sulfur bond between cytochrome c heme iron and methionine 80 sulfur atom
cytochrome c/cardiolipin complex
dynamic light scattering
small angle X-ray scattering
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Funding. This work was supported by the Russian Foundation for Basic Research (project 17-74-10248), the Ministry of Science and Higher Education within the framework of the State Budget Project for the Crystallography and Photonics Federal Scientific Research Center (development of software for analysis of SAXS data), and the ESRF BAG MX-2079 project (registration of SAXS on the BioSAXS BM29 station). The study used the equipment of the Multi-access Computing Center of the Crystallography and Photonics Federal Scientific Research Centre, Russian Academy of Sciences.
Conflict of interest. The authors declare no conflict of interest in financial or any other sphere.
Ethical approval. This article contains no studies with human participants or animals performed by any of the authors.
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