title: Mutational analysis of the N-capping box of the alpha-helix of chymotrypsin inhibitor 2.
abstract: The N-terminus of the helix of the chymotrypsin inhibitor 2 from barley (CI2) has an N-capping box (Ser at the first position in the helix and Glu at position 4) as well as a frequently found Glu at position 3. The energetic importance of this motif has been studied by determining the free energy of unfolding of the wild-type and protein mutants derived from those residues using guanidinium chloride-induced denaturation and differential scanning microcalorimetry. Mutating N-cap residue Ser31 to either Ala or Gly destabilizes CI2 by 0.8-1 kcal mol-1. Truncation of the box in the mutants SA31EA33EA34 or SG31EA33EA34 destablizes the protein by 1.5-2 kcal mol-1. The N-capping box is an important motif in stabilizing proteins and delineating the beginning of alpha-helices in the pathway of protein folding.
authors.affiliation: MRC Unit for Protein Function and Design, Cambridge Centre for Protein Engineering, UK.
authors.forename: N F
authors.initials: NF
authors.lastname: elMasry
authors.forename: A R
authors.initials: AR
authors.lastname: Fersht
mesh_terms: D002152:Calorimetry, Differential Scanning; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002918:Chymotrypsin / Q000037:antagonists & inhibitors*; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics; D019791:Guanidine; D006146:Guanidines / Q000494:pharmacology; D001467:Hordeum / Q000737:chemistry; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010455:Peptides; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D006146:Guanidines; D010455:Peptides; D010940:Plant Proteins; C093336:chymotrypsin inhibitor 2; D002918:Chymotrypsin; D019791:Guanidine