title: Switching from the unfolded to the folded state of the helix-loop-helix domain of the Id proteins based on the O-acyl isopeptide method.
abstract: The inhibitors of DNA binding and cell differentiation Id1-4 are helix-loop-helix (HLH) proteins that negatively regulate DNA transcription by forming inactive dimers with ubiquitous and tissue-specific bHLH proteins, including E47 and MyoD, respectively. Their highly conserved HLH domains are essential for heterodimerization, but can also self-associate to highly stable, alpha-helix-rich structures at low micromolar peptide concentrations. Here, we show that the introduction of an O-acyl isodipeptide unit involving the putative N-cap serine residue of the C-terminal helix completely abrogates the propensity of the Id HLH analogue for any secondary and tertiary structure, resulting in a random coil, as shown by CD measurements in nonbuffered aqueous solutions. However, the HLH fold reappears as soon as an O-->N intramolecular acyl migration, which occurs spontaneously under physiological conditions, restores the native N-cap serine residue. These results show that changes addressing the N-terminus of the C-terminal helix can dramatically influence the HLH structure, and suggest that local interactions at the junction between the loop and the C-terminal helix might be crucial during the HLH folding process. Furthermore, the present study contributes to the evaluation of the O-acyl isodipeptide unit as a powerful tool to introduce a conformational switch into peptides.
authors.affiliation: Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitätsstrasse 31, 93053 Regensburg, Germany.
authors.forename: Sebastian D
authors.initials: SD
authors.lastname: Kiewitz
authors.forename: Taeko
authors.initials: T
authors.lastname: Kakizawa
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kiso
authors.forename: Chiara
authors.initials: C
authors.lastname: Cabrele
mesh_terms: D000595:Amino Acid Sequence; D002621:Chemistry / Q000379:methods; D019281:Dimerization; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051798:Inhibitor of Differentiation Protein 1 / Q000737:chemistry; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012995:Solubility; D015533:Transcriptional Activation
chemical_list: C497453:ID1 protein, human; D051798:Inhibitor of Differentiation Protein 1; D010455:Peptides