title: Substitutions of proline 76 in yeast iso-1-cytochrome c. Analysis of residues compatible and incompatible with folding requirements.
abstract: Fine-structure genetic mapping previously revealed numerous nonfunctional cyc1 mutations having alterations at or near the site corresponding to amino acid position 76 of iso-1-cytochrome c from the yeast Saccharomyces cerevisiae. DNA sequencing of the alterations in four of these cyc1 mutations indicated that the normal Pro-76 was replaced by Leu-76. Revertants containing at least partially functional iso-1-cytochromes c were isolated, and the alterations were analyzed by DNA sequencing and protein analysis. Specific activities of the altered iso-1-cytochromes c were estimated in vivo by growth of the strains in lactate medium; compared to normal iso-1-cytochrome c with Pro-76, the following activities were associated with the following replacements: approximately 90% for Val-76, approximately 60% for Thr-76, approximately 30% for Ser-76, approximately 20% for Ile-76, and 0% for Leu-76. In order to develop an understanding of the factors that determine whether or not an altered iso-1-cytochrome c will function, we undertook a theoretical analysis which led to the conclusion that the activity of the proteins was dependent on both short- and long-range interactions. Short-range interactions were estimated from studies on known protein structures which gave the likelihood that various amino acids would be found in a local backbone configuration similar to the native protein; long-range interactions with the rest of the molecule were analyzed by considering the size of the side chain. We believe this approach can be used to analyze a wide variety of mutant proteins.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003574:Cytochrome c Group / Q000235:genetics*; D045304:Cytochromes c; D004271:DNA, Fungal; D004274:DNA, Recombinant; D009154:Mutation; D011392:Proline; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins
chemical_list: C014059:CYC1 protein, S cerevisiae; D003574:Cytochrome c Group; D004271:DNA, Fungal; D004274:DNA, Recombinant; D029701:Saccharomyces cerevisiae Proteins; D045304:Cytochromes c; D011392:Proline