FIGURE 1.

cpSRP43 makes highly sequence-specific interactions with the FDPLGL motif in the L18 sequence. A–F, alanine-scanning mutagenesis of the entire LHCP (A-C), and alanine-, glycine-, and lysine-scanning mutagenesis within the L18 sequence of LHCP (D–F). The aggregation prevention activity of cpSRP43 was assayed at 1:1 (A and D) and 1:3 (B and E) molar ratios of LHCP to cpSRP43. aa, amino acids; mut, mutant. In C and F, the disaggregase activity was measured at 1:6 molar ratio of LHCP to cpSRP43. All assays were performed in 384-well plates using a Tecan Freedom EVO liquid-handling robot, as described under “Experimental Procedures.” G and H, single-cysteine substitutions at individual residues in L18 were tested for their ability to prevent the aggregation of LHCP (G) and to resolubilize existing LHCP aggregates (H). In G, a 1:1 ratio of cpSRP43 and LHCP was used. In H, a 5:1 ratio of cpSRP43 relative to LHCP (in aggregates) was used.