Fig. 4.
SDS22 binds exclusively to metal-deficient PP1 and requires Tyr134 for productive binding. (A) SPR experiments between SDS22 and WT PP1 (PP1WT) performed either in metal-rich buffer (Left; magenta dashed box) or in metal-free buffer (Middle; gray dashed box). The SPR sensorgrams for SDS22 and PP1 in metal-rich (magenta) and metal-free (gray) buffer are shown at the right. Cartoons (Left and Middle) illustrate SPR results. Metal-loaded PP1 conformation indicated by a "closed" Tyr134 loop (light beige with closed Tyr134 loop; typically contains both the M1 and the M2 metals). The SDS22-bound conformation is shown in teal with an "open" Tyr134 loop. The SPR data show that the SDS22-bound conformation is accessible only after the M1 metal is lost (half-life of metal loss determined using SPR, SI Appendix, Fig. S4). (B) The same as A except with PP1H66K, which does not bind M1. (C) The same as A, except with PP1 bound to the cyanobacterial toxin MC, which binds the PP1 hydrophobic pocket. (D) The same as A except with PP1Y134A.