Figure 2. NMR structure, solubility, and stability of P140 and 131–151 peptides.

(A,B) Superposition of the four lowest energy structures of the non-phosphorylated and phosphorylated peptides 131–151 after simulated annealing and restrained MD calculations. For simplicity, peptide residues are numbered from 1 to 21 for the non-phosphorylated peptide (a) and phosphorylated P140 peptide (b). The phosphorylated Ser residue at position 10 (Ser¹⁴⁰) is represented by pS. For full details, see Text S1, Tables S1, S2, S3, S4, and Figures S4, S5, S6, S7. (C) Determination of the solubility limit of P140 and 131–151 peptides in distilled water, PBS and RPMI 1640 culture medium. The data show the variation of the mean intensity of light scattered (expressed as kilocounts, Kcps) that occurs when peptide aggregates are formed. In culture medium, P140 peptide aggregates at concentrations equal or superior to 50 µM. The amount and size of aggregates increase with peptide concentrations (4136±2800 nm at a 100 µM-concentration and 6972±4200 nm at a 200 µM-concentration). (D) Stability at 37°C of P140 peptide in 150 mM NaCl and PBS, as measured by high-performance liquid chromatography from the area of the peak corresponding to the intact peptide.