FIGURE 1.
15N HSQC spectrum of Sm-TSP-2-EC2. a, 15N HSQC spectrum of a 1.4 mm solution of Sm-TSP-2-EC2 in H2O at 298 K in the presence of 5 mm CHAPS. The cross-peaks of the backbone amides are assigned with the one-letter amino acid code and the sequence number of the residue. Horizontal lines connect pairs of cross-peaks from the side-chain amides of Asn and Gln. Folded peaks from arginine side chains are labeled with a star. Gly-1, Ser-2, and Asn-3 were introduced by the protein expression construct. Insets are amide cross-peaks for residues Phe-33 and Asp-46 corresponding to protein:CHAPS ratios of 1:0 (1), 1:5 (2), 1:20 (3), 1:40 (4), and 1:60 (5). b, binding affinity of Sm-TSP-2-EC2 to CHAPS measured by NMR spectroscopy at 298 K. Kd values obtained from the chemical-shift changes of Lys-22, Phe-33, Glu-35, Leu-40, Asp-46, Lys-73, and Leu-77 were 0.86 ± 0.08, 0.92 ± 0.09, 0.89 ± 0.11, 1.23 ± 0.11, 2.02 ± 0.19, 1.94 ± 0.30, and 1.16 ± 0.10 mm, respectively, indicating an upper limit of about 2.00 mm.