title: A small engineered protein lacks structural uniqueness by increasing the side-chain conformational entropy.
abstract: A small globular protein, the third repeat of the c-Myb DNA-binding domain, which is composed of 54 amino acid residues, was engineered so as to understand the structural uniqueness of native proteins. This small protein has three alpha-helices that form a helix-turn-helix structure, which is maintained by the hydrophobic core with three Ile residues. One of the mutant proteins, with two of the buried Ile (Ile-155 and Ile-181) substituted with Leu residues, showed multiple conformations, as monitored by heteronuclear magnetic resonance spectroscopy for 13C- and 15N-labeled proteins. The increase in the side-chain conformational entropy, caused by changing the Ile to a Leu residue on an alpha-helix, could engender the lack of structural uniqueness. In native proteins, the conformations of not only the beta-branched side chains, but also those of the neighboring bulky side chains, can be greatly restricted, depending upon the local backbone structure.
authors.affiliation: Biomolecular Engineering Research Institute, Osaka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Furukawa
authors.forename: M
authors.initials: M
authors.lastname: Oda
authors.forename: H
authors.initials: H
authors.lastname: Nakamura
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004268:DNA-Binding Proteins / Q000737:chemistry*; D019277:Entropy; D019077:Helix-Turn-Helix Motifs; D007532:Isoleucine; D007930:Leucine; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000737:chemistry*; D020598:Proto-Oncogene Proteins c-myb; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D015534:Trans-Activators / Q000096:biosynthesis / Q000737:chemistry*
chemical_list: D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D020598:Proto-Oncogene Proteins c-myb; D011994:Recombinant Proteins; D015534:Trans-Activators; D007532:Isoleucine; D007930:Leucine