Biology subjects

Melnik, B. S.

Publications and source records attributed to Melnik, B. S..

5 recordsLinked to original sources

bioRxiv2023

Investigation of ice nucleation properties of Pseudomonas syringae bacterium and insoluble low molecular weight substances

Control of the water freezing process is considerable in different fields of science and technology: from the artificial snow production to the cryopreservation of biological materials. To date, there is no conventional theory that predicts the influence of various biological and non-biological ice nucleators on the formation of ice and, accordingly, on the freezing point of supercooled water. In this work, we investigated the influence of bacterium Pseudomonas syringae, a biological ice nucleator, and heterodisperse insoluble powders of low molecular weight substances on the process of water freezing. AgCl, ZnO and SnO2 were found to be ice nucleators. This property has not been described previously in the literature. It has also been established that insoluble low molecular weight substances affect both the freezing point of water and the temperature of coexistence of water and ice.

biophysics↗

bioRxiv2021

A novel view on the mechanism of biological activity of antifreeze proteins

The adaptation of organisms to sub-zero temperatures is an intriguing problem in biology and biotechnology. The ice-binding antifreeze proteins are known to be responsible for the adaptation, but the mechanism of their action is still far from being clear. Here we show that: (i) in contrast to common belief, ice-binding proteins do not reduce the water freezing temperature and even raise (1) the ice melting point; (ii) at sub-zero temperatures (to {approx} -30{degrees}C), ice can be formed only on ice-binding surfaces, but, for kinetic reasons, not in bulk water; (iii) living cells have some large surfaces, which can bind the antifreeze proteins. These facts allow suggesting that the task of antifreeze proteins is not to bind to the ice crystals already formed in the cell and stop their growth or rearrangement, but to bind to those cell surfaces where the ice nuclei can form, and thus to prevent ice formation completely.

biophysics↗

bioRxiv2020

Designing and studying a mutant form of the ice-binding protein from Choristoneura fumiferana.

Ice-binding proteins are expressed in the cells of some organisms, helping them to survive extremely low temperatures. One of the problems in study of such proteins is the difficulty of isolation and purification. For example, eight cysteine residues in cfAFP from Choristoneura fumiferana (the eastern spruce budworm) form intermolecular bridges during the overexpression of this protein. This impedes the process of the protein purification dramatically. In this work we designed a mutant form of ice-binding protein cfAFP, which is much more easy to isolate that the wild-type protein. The mutant form named mIBP83 did not lose the ability to bind to ice surface. Besides, observation of the processes of freezing and melting of ice in presence of mIBP83 showed that this protein affects the process of ice melting, increasing its melting temperature, and at least does not decrease the freezing temperature.

molecular biology↗

bioRxiv2019

Loops linking secondary structure elements affect the stability of molten globule intermediate state of apomyoglobin

Apomyoglobin is a protein widely used as a model for studying globular protein folding. This work aimed to test the hypothesis on influence of rigidity and length of loops linking protein secondary structure elements on the stability of molten globule intermediate state. For this purpose, we studied folding/unfolding of mutant apomyoglobin forms with substitutions of proline residues to glycine and with loops elongated by three and six glycine residues. For all the protein forms, denaturation/renaturation kinetic curves at different urea concentrations were obtained, folding/unfolding constants were calculated and dependencies of rate constant logarithms on urea concentrations were plotted. All the data gave an opportunity to calculate free energies of different apomyoglobin states. As a result, the mutations in apomyoglobin loops were demonstrated to have a real effect on intermediate state stability compared to unfolded state.

biophysics↗

bioRxiv2019

GFP fusion protein with embedded foreign peptide

From the point of view structural biology and protein engineering the green fluorescent protein (GFP) is an exceptionally attracting object. The tertiary structure of GFP is quite unique: it reminds a "cylinder" or a "barrel" consisting of beta-layers that contains an alpha-helix inside. The "barrel" is a special container for an alpha-helix serving to protect the latter from the influence of the surroundings. Therefore a reasonable question arises whether the "barrel" can function as a container for preservation and isolation of other peptides. The alpha-helix itself contains hydrophilic amino acids, whereas inside the barrel there are many molecules of bound water. We supposed that the central alpha-helix of green fluorescent protein could be substituted for foreign peptide. In this study we checked the possibility for creation of such a system on base of GFP, where the toxic peptide is isolated from the environment inside the protein. The modification of green fluorescent protein was carried out. An antimicrobial peptide was inserted into the central alpha-helix. The results of our experiments show that such a chimeric protein is compact, soluble and non-toxic for the producing cell culture, but its structure is destabilized. The obtained data show that the idea of use of green fluorescent proteins as a < > for storing foreign peptides could be realized.

bioengineering↗