Figure 5. NMR-derived motional order parameters.
Order parameters, S2, for lactose-free (A) and lactose-loaded (B) Gal-7 P4 trans-states vs. the amino acid sequence. (C) The difference in order parameters, ΔS2 [calculated as S2 for lactose-free minus S2 for lactose-loaded protein] is shown vs. the Gal-7 amino acid sequence. These terms were derived from T1 and T2 relaxation times and NOE values determined at 600 and 800 MHz and analyzed by using the Lipari–Szabo model free approach as discussed in the text. A positive ΔS2 value indicates more restricted motion for an NH vector of that residue in the lactose bound state, and a negative ΔS2 value indicates less restricted motion for an NH vector in that residue in the lactose bound state. (D) Crystallographic structure of Gal-7 (PDB access code 4GAL) highlights differences shown in panel (C), with negative ΔS2 values highlighted in shades of red and positive ΔS2 values highlighted in shades of blue. Gray indicates not significant change. A molecule of bound lactose is shown in yellow for structural orientation.