Inhibitor binding to Plm determined by NMR. (A) Saturation-transfer difference (STD) spectra reveal binding of TXA to μPlm. The top line (blue) shows the reference spectrum of TXA alone. The middle line (green) shows the STD signals of TXA in the presence of μPlm; positive STD signal at 2.6 and 2.58 ppm of TXA with an intensity of 5% is indicative of TXA binding to μPlm. The bottom line (red) shows the STD spectrum in the absence of μPlm; there are no signals, as expected. (B) Purcell-Meiboom-Gill (CPMG) spectra confirm binding of TXA to μPlm. TXA signals are compared in the presence (green) and absence (red) of μPlm. TXA binding to μPlm is indicated by the reduction in peak intensity in the presence of μPlm. (C) CPMG spectra of lysine. The ligand signals in the presence of μPlm (green) at 2.8 to 2.75 ppm are attenuated, which indicates binding. (D) CPMG spectra of YO-2 as a positive control. The binding of the μPlm (green) leads to a reduction of signals and also a shift of the signal at 7.25, 6.94, and 6.75 ppm, which indicates strong binding of YO-2 to μPlm. (E) CPMG spectra of methionine as a negative control. In the presence of μPlm (green), the change of the intensity is insignificant, suggesting that methionine does not bind to μPlm.