title: Effect of helix length on the stability of the Lac repressor antiparallel coiled coil.
abstract: The helix length dependence of the stability of antiparallel four-chain coiled coils is investigated using eight synthetic peptides (Lac21-Lac28) whose sequences are derived from the tetramerization domain of the Lac repressor protein. Previous studies using analytical ultracentrifugation sedimentation equilibrium experiments to characterize Lac21 and Lac28 justifies the use of a two state model to describe the unfolding behavior of these two peptides. Using circular dichroism spectropolarimetry as a measure of tetramer assembly, both chemical and thermal denaturation experiments were carried out to determine thermodynamic parameters. We found that the hydrophobic core residues provide the greatest impact on stability and, as a consequence, must reorganize the register of the antiparallel helices to accommodate the burial of the nonpolar amino acids. Addition of noncore residues appears to have only a minor effect on stability, and in some cases, show a slight destabilization.
authors.affiliation: Neural Pathways Discovery Performance Unit, GlaxoSmithKline, 11 Biopolis Way, The Helios #03-1/02, Singapore 138667.
authors.forename: Wheaton
authors.initials: W
authors.lastname: Little
authors.affiliation: Department of Pharmaceutical Sciences, University of Colorado School of Pharmacy, 12850 E. Montview Blvd., Aurora, CO, 80045.
authors.forename: James P
authors.initials: JP
authors.lastname: Robblee
authors.affiliation: Department of Biology, Western Washington University, Bellingham, WA, 98225.
authors.forename: Caroline L
authors.initials: CL
authors.lastname: Dahlberg
authors.affiliation: Department of Biology, Haverford College, 370 Lancaster Ave, Haverford, PA, 19041.
authors.forename: Bashkim
authors.initials: B
authors.lastname: Kokona
authors.affiliation: Department of Biology, Haverford College, 370 Lancaster Ave, Haverford, PA, 19041.
authors.forename: Robert
authors.initials: R
authors.lastname: Fairman
mesh_terms: D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D056968:Lac Repressors / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D055550:Protein Stability; D017433:Protein Structure, Secondary
chemical_list: D029968:Escherichia coli Proteins; D056968:Lac Repressors; C539064:LacI protein, E coli; D010455:Peptides
keywords: Lac repressor; analytical ultracentrifugation; antiparallel coiled coil; circular dichroism; homotetramer; protein design; thermodynamic analysis