Figure 3.

a) Relaxation rates in the rotating frame, R _1ρ(¹⁵N_ϵ), for UmpK arginine side‐chains in the nucleotide‐free form (green), AP₅U complex (red) and TSA complex (blue). For the TSA complex the relaxation rates were derived from the ¹H‐detected experiments, for the AP₅U complex the rates were derived from both the ¹³C‐detected and the ¹H‐detected experiments, whereas for the nucleotide‐free form the rates were derived from ¹³C‐detected experiments only (Supporting Information). b) Order parameters S ^2, describing pico‐nanosecond motions of UmpK arginine side‐chains in the nucleotide‐free form (green), AP₅U complex (red) and TSA complex (blue), were obtained from global analyses of the available ¹⁵N_ϵ relaxation data (Table S2) using the model‐free approach.13 c) Conformational heterogeneity of UmpK arginine side‐chains in the AP₅U complex (left) and in the TSA complex (right). The order parameters S ² shown in (b) were mapped on the respective crystal structures (AP₅U, PDB: 1UKE;11 TSA, PDB: 3UKD7). All parameters obtained from the global analysis of the relaxation data are given in Table S3.