title: Mutational studies of protein stability and folding of the hyperstable MYL Arc repressor variant.
abstract: The Arc-MYL variant is hyperstable and has an earlier transition state than wild type as a consequence of replacing the wild-type salt-bridge triad formed by R31, E36 and R40 with hydrophobic interactions formed by M31, Y36 and L40. Amino acid substitution mutations were constructed at 16 positions in the Arc-MYL background and the equilibrium stabilities of the corresponding mutant proteins were determined. At three positions, mutations were found to be less destabilizing in MYL than in wild-type Arc, and, at one position, the opposite result was obtained. The kinetics of refolding and unfolding were determined for a subset of the Arc-MYL core mutants. Three mutations--VA18, LA19 and LA40--had their major energetic effects on the refolding rate. The interactions perturbed by these mutations appear to be substantially formed in the transition state. V18 and L19 are in the N-terminal turn of helix A and L40 is in the center of helix B. The remaining mutations--VA22, MA31, VA33, YA36, VA41, MA42 and FA45--had some effects on refolding but exerted their major effects on the unfolding rate. Approximately 30% of the energetic interactions mediated by these latter side chains seem to be present in the transition state of Arc-MYL.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Alok K
authors.initials: AK
authors.lastname: Srivastava
authors.forename: Robert T
authors.initials: RT
authors.lastname: Sauer
mesh_terms: D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000235:genetics; D009687:Nuclear Proteins; D011487:Protein Conformation; D017510:Protein Folding; D012097:Repressor Proteins / Q000737:chemistry* / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics; D025521:Tumor Suppressor Proteins; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics; D054334:Viral Regulatory and Accessory Proteins
chemical_list: D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins