Valery Ya. Grinberg

Glass transition temperature of proteins. Calculation based on the additive contribution method and experimental data

A method for calculating the glass transition temperature for a protein from its amino acid composition is proposed. Results of calculations for 32 food proteins are in agreement with the experimental data. The contribution of disulphide cross-links and the length of the protein polypeptide chain to its glass transition temperature is estimated.

Effects of polysaccharides upon the functional properties of 11 S globulin of broad beans

Abstract The effect of polysaccharides upon the conformational stability, emulsifying properties and thermal gelation ability of the 11 S globulin (legumin) from broad beans under conditions of both protein-polysaccharide incompatibility and complex formation has been investigated. Under conditions of incompatibility (pH 7·6 for carboxyl-containing and neutral polysaccharides) the conformational stability of the legumin is not changed by the presence of the polysaccharides. At the same time a significant decrease in the emulsifying threshold and an increase in the stability of oil-in-water emulsions, stabilized by the protein, as well as some decrease in the gelation threshold in the presence of polysaccharides have been observed. Under conditions of legumin-polysaccharide complex formation (pH 4·2–6·0, low ionic strength for carboxyl- and sulphate-containing polysaccharides) a significant decrease in the temperature and enthalpy of legumin denaturation as well as a decrease in the minimum biopolymer concentration required for emulsions formation and an increase in emulsion stability have been observed. As a rule, legumin-polysaccharide complexes were poorly soluble even at a substantial excess of polysaccharide. Their solubility which was independent of the method of mixing was a limiting factor for preparing gels and stable foams on using these complexes.

Biomembrane sensitivity to structural changes in bound polymers.

Anionic liposomes containing a 4:1 molar ratio of neutral to anionic phospholipids were treated with an excess of five zwitterionic polymers differing only in the spacer length separating their cationic and anionic moieties. Although the polymers do not disrupt the structural integrity of the liposomes, they can induce spacer-dependent molecular rearrangements within the liposomes. Thus, the following were observed: spacer length = 1, no binding to the liposomes; spacer length = 2, adsorption to the liposomes, but no molecular rearrangement; spacer length = 3, lateral lipid segregation but little or no flip-flop; spacer length = 4 or 5, lateral lipid segregation and flip-flop. These diverse behaviors are relevant to the use of biomedical formulations where polyelectrolytes play a role.

Cloning, sequencing, expression, and characterization of thermostability of oligopeptidase B from Serratia proteamaculans, a novel psychrophilic protease

Protease from Serratia proteamaculans (PSP) is the first known psychrophilic oligopeptidase B. The gene of S. proteamaculans 94 oligopeptidase B was cloned, sequenced and expressed in Escherichia coli. The unfolding of PSP molecule following heat treatment at 37°C by measuring fluorescence spectra was examined in parallel with the residual activity determination. The effect of PSP thermostabilization by glycerol at 37-50 °С was revealed. Calcium ions and buffer solution of low molarity cause the opposite effect - the acceleration of PSP inactivation at 37°C. The thermal stability of PSP molecule in the presence of 0-100mM CaCl2 was also investigated by means of high-sensitivity differential scanning calorimetry. The artificial reconstruction of the natural complex PSP-chaperonin from S. рroteamaculans was carried out: the stable complex (1:1) of chaperonin E. сoli GroEL with active recombinant enzyme PSP was obtained. It was shown that complex formation with chaperonin promotes PSP thermostability at 37°C.

Effects of pH upon the liquid-liquid phase equilibria in solutions of legumins and vicilins from broad beans and peas

Abstract The effects of pH on the liquid-liquid phase equilibria in solutions of legumins and vicilins from broad beans and peas were investigated. It was shown that for these systems the dependence of solution-critical temperature on pH is at a maximum near the isoelectric point of the protein. This function shifts to the region of lower pH values and temperatures at high concentrations of sodium chloride. The shape of the function is controlled by the balance of dipole-dipole and electrostatic interactions between the protein molecules. Another significant factor of phase equilibria in the systems investigated is the binding of chloride anions with protein molecules which determines the protein isoelectric point.

Cryostructuring of polymer systems. 44. Freeze-dried and then chemically cross-linked wide porous cryostructurates based on serum albumin

Abstract Spongy cryostructurates based on bovine serum albumin (BSA) have been prepared via freezing the aqueous solutions of the protein followed by freeze-drying and subsequent cross-linking BSA macromolecules each together within the macropore walls using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) dissolved in ethanol. The gel-fraction yield values testifies high efficiency (>93%) of the protein building-up into the 3D polymeric network. Poor swelling of the pore walls of BSA-based sponges in water (1–2 g H2O per 1 g of dry polymer) and even in the powerful protein-solubilizing media (8 m urea, 5 m guanidine hydrochloride, 1% SDS) indicates the multipoint character of albumin cross-linking via the pendant peptide bonds. As a result, strong cross-linking is able (as revealed by HS-DSC) to inhibit BSA thermal denaturation. The size of wide pores in the obtained cryostructures ranges from 40 to 250 μm and mainly depends on the freezing temperature.