Abstract
The main structural protein of the human eye, which accounts for about 50 % of the mass of all water-soluble proteins comprising the lens, is α-crystallin. Alpha-crystallin functions as a molecular chaperone, preventing other lens crystallins from interfering in the vital activity. Alpha-crystallins partially or fully stabilise unfolded proteins, preventing the formation of deposits, helping to preserve the lens transparency and reducing the risk of a number of diseases, including cataracts. This biological phenomenon can be considered in the framework of materials science when considering the problem of slowing down the aging processes of polymers. In the present study, methods for slowing down the process of aggregation of α-lactalbumin in solution are considered, using the binary system α-lactalbumin–αA-crystallin as an example. To this end, experimental data on the rate of change of the aggregation process were formalised, i.e. expressed in terms of transition temperatures and plasticisation functions of the components. The proposed expressions make it possible to clarify the concentration dependence of the initial aggregation rate, its order, and also to quantify the effect of the dose of UV irradiation on the aging process of the system. The experimentally obtained result means that an increase in the content of α-crystallin leads to an additional blocking of hydrogen bonds in the surface layers of α-lactalbumin and, accordingly, to an increase in the plasticising effect. In addition, the obtained expression of the activation energy of polymer chain rearrangement helps to account for the influence of infrared radiation on the development of so-called thermal cataracts (usually occurring in glassblowers, steelmakers, blacksmiths, welders, etc.), when the etiological factor consist in infrared rays having wavelengths from 0.74 to 2.50 microns, which freely pass through the cornea and iris without damaging them, and are largely adsorbed by the lens, causing its overheating.
Highlights
Binary biopolymer systems, such as proteinprotein and protein-polysaccharide formations, are widespread in nature
Refinement of the concentration dependence of the initial aggregation rate and the physical meaning of the parameters included therein An empirical expression for determining the initial aggregation rate of v as a function of x was proposed in [5]:
In order to establish the dependence of the coefficient АСо on the characteristic temperatures of the polypeptides of the system αA-crystallin and α-lactalbumin, we use the theory of absolute reaction rates [8] in calculating v: v kT 2
Summary
Binary biopolymer systems, such as proteinprotein and protein-polysaccharide formations, are widespread in nature. One of the natural mechanisms of inhibition of cataract development in the human eye is associated with the presence of the α-crystallin protein in the lens, which performs a molecular chaperone role – in this case, preventing the aggregation of β-crystallin and thereby preventing the development of cataracts [4]. In this case, the α-crystallin molecules permeate into a β-crystallin structure that has denatured under the influence of UV radiation, permeating it and reducing the β-crystallin thermal aggregation rate. The eye lens protein αA-crystallin, consisting of 173 amino acid residues (AAR), belongs to the family of small heat shock proteins (sHSPs), having a molecular weight of about 20 000 g/mol
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