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Figure 1.
Figure 1: Double-mutant cycles for hydrogen-bonding interactions
in bacteriorhodopsin. For each cycle shown, the difference in
free energies of unfolding (black number by the arrow) was
measured for the pair of proteins connected by the arrow. Free
energies of unfolding are compared at an SDS concentration at
which the wild-type protein (WT) is 50% unfolded to minimize
extrapolations needed. Errors are s.d. for three separate
measurements. Next to each double-mutant cycle is a close-up
view of the relevant hydrogen bond shown as blue dotted line
between the altered side chains along with the heavy atom
donor–acceptor distance. Donor and acceptor residues are
labelled in green and blue, respectively. Donor–acceptor
distinction in the two strongest interactions was arbitrary. On
the basis of hydrogen-bonding patterns and nearest neighbours,
it seems that all the potentially charged residues are the
neutral species. The inset (bottom right) shows the location of
each interaction in the context of the protein (PDB ID 1C3W).
The planes of green dots indicate the estimated position of the
edge of the hydrocarbon region of the bilayer as defined
previously^28. Any interaction mediated by the residues that
contain at least one atom in the hydrocarbon region is mapped
with the red line, and the interaction in the lipid/water
interface region is mapped with a blue line.
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