Equilibrium unfolding experiments on several mutant forms of horse heart cytochrome c were performed. By means of absorbance spectroscopy, the accumulation of an equilibrium intermediate was revealed upon unfolding of Y97V mutant protein, and its structural properties were characterized. The data obtained allow one to conclude that the equilibrium intermediate corresponds to the earliest kinetic intermediate Ic in cytochrome c folding reaction. A comparative analysis of spectral properties of unfolded states of cytochrome c induced by urea or guanidine hydrochloride is presented.

Amino Acid Substitution↗

PubMedDate not supplied

[De novo proteins with a given spatial structure: new approaches to design and analysis].

Based on the molecular theory of protein structure the de novo protein was designed in order to obtain the tertiary fold which has not yet been observed in natural proteins, namely four-stranded antiparallel beta-sheet covered by two alpha-helixes. The gene coding for this protein (named albebetin) was chemically synthesized, cloned in plasmid with SP6 phage promoter and expressed in mRNA-dependent cell-free translation system. An approach was developed to study albebetin using only nanogram amounts of radio labelled protein without previous purification. The preliminary analysis of its structure by gel-filtration, urea-gradient electrophoresis and limited proteolysis revealed compactness and stability of the de novo protein.

Amino Acid Sequence↗

PubMedDate not supplied

Thermodynamic parameters of helix-random coil transitions in polypeptide chains. IV. Random copolymers of L-alanine with L-glutamic acid.

pH-Induced helix-random coil transitions in random copolymers of Ala with Glu have been investigated in order to determine the effect of Ala on the stability of the helical state of polyglutamic acid. The free energies for the transfer of one uncharged Glu residue from a random coil to a helix (deltaGo) have been determined from potentiometric titration curves by the method of Zimm and Rice. It has been shown that the introduction of Ala hampers the transfer of a Glu residue from a random coil to a helix (reduces -deltaGo), although Ala itself is a helix-forming residue, i.e., its free energy decreases during helix formation. This has suggested that its introduction weakens the helix-stabilizing interactions between the uncharged Glu residues (apparently hydrogen bonds). The evaluation of the intrinsic helix-random coil equilibrium constant s for uncharged Glu residues with consideration of this situation yields a value which is smaller than the value of s for (Glu)n and in good agreement with the theoretical values.

Alanine↗