Two different recombinant constructs of the N-terminal
domain in Escherichia coli DnaJ were uniformly
labeled with nitrogen-15 and carbon-13. One, DnaJ(1–78),
contains the complete “J-domain,” and the other,
DnaJ(1–104), contains both the “J-domain”
and a conserved “G/F” extension at the C-terminus.
The three-dimensional structures of these proteins have
been determined by heteronuclear NMR experiments. In both
proteins the “J-domain” adopts a compact structure
consisting of a helix-turn-helix-loop-helix-turn-helix
motif. In contrast, the “G/F” region in DnaJ(1–104)
does not fold into a well-defined structure. Nevertheless,
the “G/F” region has been found to have an
effect on the packing of the helices in the “J-domain”
in DnaJ(1–104). Particularly, the interhelical angles
between Helix IV and other helices are significantly different
in the two structures. In addition, there are some local
conformational changes in the loop region connecting the
two central helices. These structural differences in the
“J-domain” in the presence of the “G/F”
region may be related to the observation that DnaJ(1–78)
is incapable of stimulating the ATPase activity of the
molecular chaperone protein DnaK despite evidence that
sites mediating the binding of DnaJ to DnaK are located
in the 1–78 segment.