Nonnative Helical Motif in a Chaperone-Bound Protein Fragment

¹ University of Wisconsin-Madison
² University of Wisconsin - Madison

^* To whom correspondence should be addressed. E-mail: cavagnero{at}chem.wisc.edu.

Submitted on December 11, 2007
Revised on December 14, 2007
Accepted on 20 December 2007

	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-, is employed as a chaperone model. By taking advantage of the improved spectral quality resulting from chaperone deuteration, we find that DnaK--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, the presence of a nonnative helical motif in a large chaperone-bound protein fragment under physiologically relevant solution conditions.

Key Words: DnaK, apomyoglobin, chaperones, nonnative helicity, protein folding