title: Reducing lambda repressor to the core.
abstract: Lambda repressor fragment λ(*)(6-85) is one of the fastest folding small protein fragments known to date. We hypothesized that removal of three out of five helices of λ(*)(6-85) would further reduce this protein to its smallest folding core. Molecular dynamics simulations singled out two energetically stable reduced structures consisting of only helices 1 and 4 connected by a short glycine/serine linker, as well as a less stable control. We investigated these three polypeptides and their fragments experimentally by using circular dichroism, fluorescence spectroscopy, and temperature jump relaxation spectroscopy to gain insight into their thermodynamic and kinetic properties. Based on the thermal melts, the order of peptide stability was in correspondence with theoretical predictions. The most stable two-helix bundle, λ(blue1), is a cooperatively folding miniprotein with the same melting temperature and folding rate as the full-length λ(*)(6-85) pseudo wild type and a well-defined computed structure.
authors.affiliation: Department of Chemistry, University of Illinois, Urbana, Illinois 61801, USA.
authors.forename: Maxim B
authors.initials: MB
authors.lastname: Prigozhin
authors.forename: Krishnarjun
authors.initials: K
authors.lastname: Sarkar
authors.forename: Dennis
authors.initials: D
authors.lastname: Law
authors.forename: William C
authors.initials: WC
authors.lastname: Swope
authors.forename: Martin
authors.initials: M
authors.lastname: Gruebele
authors.forename: Jed
authors.initials: J
authors.lastname: Pitera
mesh_terms: D000595:Amino Acid Sequence; D030562:Databases, Protein; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D017510:Protein Folding; D017433:Protein Structure, Secondary; D058767:Protein Unfolding; D012097:Repressor Proteins / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D054334:Viral Regulatory and Accessory Proteins / Q000737:chemistry*
chemical_list: D010446:Peptide Fragments; D012097:Repressor Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins