Backbone dynamics of the N-terminal domain in E. coli DnaJ determined by ¹⁵N- and ¹³CO-relaxation measurements

The backbone dynamics of the N-terminal domain of the chaperone protein Escherichia coli DnaJ have been investigated using steady-state ¹H-¹⁵N NOEs, ¹⁵N T₁, T₂, and T(1ρ) relaxation times, steady-state ¹³C(α- 13)CO NOEs, and ¹³CO T₁ relaxation times. Two recombinant constructs of the N-terminal domain of DnaJ have been studied. One, DnaJ(1-78), contains the most conserved 'J-domain' of DnaJ, and the other, DnaJ(1-104), includes a glycine/phenylalanine rich region ('G/F' region) in addition to the 'J- domain'. DnaJ(1-78) is not capable of stimulating ATP hydrolysis by DhaK, despite the fact that all currently identified sites responsible for DnaJ- DnaK interaction are located in this region. DnaJ(1 104), on the other hand, retains nearly the full ATPase stimulatory activity of full length DnaJ. Recently, a structural analysis of these two molecules was presented in an effort to elucidate the origin of their functional differences [Huang, K., Flanagan, J. M., and Prestegard, J. H. (1999) Protein Science 8, 203-214]. Herein, an analysis of dynamic properties is presented in a similar effort. A generalized model-free approach with a full treatment of the anisotropic overall rotation of the proteins is used in the analysis of measured relaxation parameters. Our results show that internal motions on pico- to nanosecond time scales in the backbone of DnaJ(1-78) are reduced on the inclusion of the 'G/F' region, while conformational exchange on micro- to millisecond time scales increases. We speculate that the enhanced flexibility of residues on the slow time scale upon the inclusion of the 'G/F' region could be relevant to the ATPase stimulatory activity of DnaJ if an 'induced- fit' mechanism applies to DnaJ-DnaK interactions.