Figure 1.

The crystal structure of E. coli adenylate kinase and three pairs of sites that were labeled to test the experimental method. (Circles each represent one double-labeled mutant, in which the donor Trp residue is represented by a green space-filling structure and the Cys residue, the site for attachment of the acceptor, is represented by a red space-filling structure.) Expected mean distance between the labeled sites in the folded state (as represented by orange lines connecting to site centers). To see this figure in color, go online.