FIGURE 4.

The β6/β7 loop is immobilized when the enzyme binds to the sorting signal. a, the order parameters (S²) for backbone amides plotted as a function of residue number. Data for apo-SrtA_ΔN59 (gray) (56) and the SrtA_ΔN59-LPAT* complex (black) are shown. Data for each residue are indicated by a filled circle and are connected by lines to emphasize trends. Secondary structural elements present in SrtA_ΔN59 are shown above the graph. b, plot of R_ex values determined from the model-free analysis as a function of residue number. A gradient shaded bar indicates residues whose resonances are very weak in the NMR spectra of apo-SrtA_ΔN59, presumably because of line broadening caused by conformational exchange (Arg¹⁵⁹ to Val¹⁶¹). The data are color-coded as in a.