title: Characterization of large peptide fragments derived from the N-terminal domain of the ribosomal protein L9: definition of the minimum folding motif and characterization of local electrostatic interactions.
abstract: A set of peptides derived from the N-terminal domain of the ribosomal protein L9 (NTL9) have been characterized in an effort to define the minimum unit of this domain required to fold and to provide model peptides for the analysis of electrostatic interactions in the unfolded state. NTL9 is a 56-residue alpha-beta protein with a beta1-loop-beta2-alpha1-beta3-alpha2 topology. The beta-sheet together with the first helix comprise a simple example of a common supersecondary motif called the split beta-alpha-beta fold. Peptides corresponding to the beta1-loop-beta2 unit are unstructured even when constrained by an introduced disulfide. The pK(a)s of Asp-8 and Glu-17 in these peptides are slightly lower than the values found for shorter peptides but are considerably higher than the values in NTL9. A 34-residue peptide, which represents the beta1-loop-beta2-alpha1 portion of NTL9, is also unstructured. In contrast, a 39-residue peptide corresponding to the entire split beta-alpha-beta motif is folded and monomeric as judged by near- and far-UV CD, two-dimensional NMR, ANS binding experiments, pK(a) measurements, and analytical ultracentrifugation. The fold is very similar to the structure of this region in the intact protein. Thermal and urea unfolding experiments show that it is cooperatively folded with a DeltaG degrees of unfolding of 1.8-2.0 kcal/mol and a T(m) of 58 degrees C. This peptide represents the first demonstration of the independent folding of an isolated split beta-alpha-beta motif, and is one of only four naturally occurring sequences of fewer than 40 residues that has been shown to fold cooperatively in the absence of disulfides or ligand binding.
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, USA.
authors.forename: Jia-Cherng
authors.initials: JC
authors.lastname: Horng
authors.forename: Viktor
authors.initials: V
authors.lastname: Moroz
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Rigotti
authors.forename: Robert
authors.initials: R
authors.lastname: Fairman
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Raleigh
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000737:chemistry; D002942:Circular Dichroism; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009282:Naphthalenesulfonates / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012269:Ribosomal Proteins / Q000138:chemical synthesis / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D055672:Static Electricity
chemical_list: D009282:Naphthalenesulfonates; D010446:Peptide Fragments; D012269:Ribosomal Proteins; C049650:ribosomal protein L9; C031762:1-naphthylamine-8-sulfonic acid; D001224:Aspartic Acid; D018698:Glutamic Acid; D008239:Lysine