The influence of amino acid substitutions on the conformational energy of cytochrome c

Single amino acid substitutions producing instability of globular proteins. Calculation of their frequencies in the entire mutational spectra of the alpha- and beta-subunits of human hemoglobin

The frequencies of substitutions resulting in protein instability were calculated by a method estimating changes in stability produced by amino acid substitutions. The method takes into account the accessibility of an amino acid position to a solvent and changes in the specificity of amino acid interactions. When tested on human mutant hemoglobins, the method yielded predictions with a preciseness of 80%. The consideration of the evolutionary homologous proteins in the analysis allowed us to estimate the evolutionary constraints imposed on stability of their spatial structure. With these limitations, approximately 50% of amino acid substitutions in the entire mutational spectra of the alpha- and beta-subunits of human hemoglobin were found to damage the spatial structure of the globular proteins.

Analysis of the factors and implications of an empirical method for estimating the stability of mutant human haemoglobins

An empirical method for estimating the effects of single amino acid substitutions on structural stability of proteins with known spatial structure is developed. Twenty physical and chemical properties of amino acids and characteristics of protein tertiary structure were analysed to determine those most involved in producing instability. We employed data on 330 mutant variants of the alpha- and beta-subunits of human haemoglobin in choice of the parameters of the method developed which yielded a 81% of prediction accuracy of stability estimates for human mutant haemoglobins.

The effects of mutations, deletions and insertions of single amino acids on the three-dimensional structure of globins

Using the method of calculation of low energy packings of alpha-helices, we studied the effects of mutations, deletions and insertions of amino acids on the structure of sperm whale myoglobin. It was found that these events can cause complete breakdown of this structure.

Reinvestigation of the primary structures of red deer and roe deer pancreatic ribonuclease and proline sites in mammalian ribonucleases

The sequences of amino acid residues 15-23 of red deer (Cervus elaphus) and roe deer (Capreolus capreolus) pancreatic ribonuclease and the identity of residue 99 in roe deer ribonuclease are corrected. Earlier results are explained by the cleavage of an Asp-Pro bond in both enzymes during the treatment with CNBr in 70% formic acid and by wrong interpretations of amino acid analyses. Proline residues, which occur at a number of positions in several mammalian ribonucleases, can be accommodated in a model of bovine ribonuclease S without disrupting the conformation of the main chain.

The structure of two alanine containing ferrichromes: sequence determination by proton magnetic resonance

Metal coordination confers an extraordinary structural stability to the ferrichromes which, independent of their variable amino acid composition, results in a basically unperturbed conformation for all the homologous peptides in the series. The proton magnetic resonance (pmr) characteristics for Al3+ analogues (alumichromes) reflect this conformational isomorphism in usual solvents so that single site substitutions are clearly recognized in the pmr spectra. Thus, the substitution of glycine by L-alanine or L-serine introduce new resonances characteristic of the sidechains and alter the pattern of the amide NH pmr region in that doublets substitute for glycyl triplets at the same site. Since for glycine- and L-serine containing alumichromes the resonances have already been identified, it is possible to unequivocally establish the primary structure of the two L-alanyl homologues ferrichrome C (see article) and sake colorant A (see article) on the basis of the comparative pmr spectra of their Al3+ analogues, namely, alumichrome C and alumisake. The resonance assignment, and hence the site occupancy, is substantiated by the temperature coefficients of the NH chemical shifts, rates of 1H-2H exchange and homonuclear proton spin decoupling experiments centered on the NH spectral region. Occupancy of site 1 by a glycine residue is observed for all known ferrichromes, which serves to conserve a "hairpin" turn. This method of obtaining sequence information should prove of general use for other systems of homologous polypeptides, provided their conformations are not affected by the residue substitutions.