title: Nonnative helical motif in a chaperone-bound protein fragment.
abstract: The effect of cotranslationally active chaperones on the conformation of incomplete protein chains is poorly understood. The secondary structure of a 77-residue chaperone-bound N-terminal protein fragment corresponding to the first five helices (A-E) of apomyoglobin (apoMb(1-77)) is investigated here at the residue-specific level by multidimensional NMR. The substrate-binding domain of DnaK, DnaK-beta, is employed as a chaperone model. By taking advantage of the improved spectral quality resulting from chaperone deuteration, we find that DnaK-beta-bound apoMb(1-77) displays a region of nonnative helicity at residues away from the main chaperone binding site. The nonnative structural motif comprises portions of the native D and E helices and has similar characteristics to the reported nonnative DE helical region of acid-unfolded full-length apoMb. Upon incorporation of the missing C-terminal amino acids, a structural kink develops between residues 56 and 57, and two separate native D and E helices are generated. This work highlights, for the first time to our knowledge, the presence of a nonnative helical motif in a large chaperone-bound protein fragment under physiologically relevant solution conditions.
authors.forename: Neşe
authors.initials: N
authors.lastname: Kurt
authors.forename: Silvia
authors.initials: S
authors.lastname: Cavagnero
mesh_terms: D020816:Amino Acid Motifs; D001059:Apoproteins / Q000737:chemistry* / Q000648:ultrastructure*; D008956:Models, Chemical; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry* / Q000648:ultrastructure*; D011487:Protein Conformation
chemical_list: D001059:Apoproteins; D009211:Myoglobin; C010857:apomyoglobin