Vakhtang V Loladze

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The small globular protein, ubiquitin, contains a pair of oppositely charged residues, K11 and E34, that according to the three-dimensional structure are located on the surface of this protein with a spatial orientation characteristic of a salt bridge. We investigated the strength of this salt bridge and its contribution to the global stability of the(More)
We have characterized the guanidine-induced unfolding of both yeast and bovine ubiquitin at 25 degrees C and in the acidic pH range on the basis of fluorescence and circular dichroism measurements. Unfolding Gibbs energy changes calculated by linear extrapolation from high guanidine unfolding data are found to depend very weakly on pH. A simple explanation(More)
A simple theoretical model for increasing the protein stability by adequately redesigning the distribution of charged residues on the surface of the native protein was tested experimentally. Using the molecule of ubiquitin as a model system, we predicted possible amino acid substitutions on the surface of this protein which would lead to an increase in its(More)
Engineering proteins to withstand a broad range of conditions continues to be a coveted objective, holding the potential to advance biomedicine, industry, and our understanding of disease. One way of achieving this goal lies in elucidating the underlying interactions that define protein stability. It has been shown that the hydrophobic effect, hydrogen(More)
In this paper we address the question of whether the burial of polar and nonpolar groups in the protein locale is indeed accompanied by the heat capacity changes, DeltaC(p), that have an opposite sign, negative for nonpolar groups and positive for polar groups. To accomplish this, we introduced amino acid substitutions at four fully buried positions of the(More)
Effects of amino acid substitutions at four fully buried sites of the ubiquitin molecule on the thermodynamic parameters (enthalpy, Gibbs energy) of unfolding were evaluated experimentally using differential scanning calorimetry. The same set of substitutions has been incorporated at each of four sites. These substitutions have been designed to perturb(More)
The contribution of solvent-exposed charged residues to protein stability was evaluated using ubiquitin as a model protein. We combined site-directed mutagenesis and specific chemical modifications to first replace all Arg residues with Lys, followed by carbomylation of Lys-amino groups. Under the conditions in which all carboxylic groups are protonated (at(More)
The C' position of the C-capping box is the second residue outside of the helix. Statistical analysis of residue distribution at the C' position in the alpha-helices' C-capping box showed that different amino acid residues occur with different probabilities, with the strongest preference being for glycine. To understand the physico-chemical basis for this(More)
Using computational and sequence analysis of bacterial cold shock proteins, we designed a protein (CspB-TB) that has the core residues of mesophilic protein from Bacillus subtilis(CspB-Bs) and altered distribution of surface charged residues. This designed protein was characterized by circular dichroism spectroscopy, and found to have secondary and tertiary(More)
Statistical analysis of the residue separation between a pair of ionizable side chains within 4 Å of each other was performed on a set of 1560 non-homologous PDB structures. We found that the frequency of pairs of like charges (i.e., pairs consisting of acidic residues Asp and Glu or pairs consisting of basic residues Arg and Lys) is two orders of magnitude(More)