Fig. 4: Modular organization regulates the dynamics of the PopZ condensate.
a The predicted radius of gyration (RG) for a half linker (IDR-40, 40 aa) (light blue), full wildtype linker (IDR-78, 78 aa) (gray), and a double linker (IDR-156, 156 aa) (dark blue). b PopZ linker expands beyond the denatured limit. The expected RG of denatured proteins as a function of the number of amino acids is shown in black91. Dimensions of PopZ-like linkers with varying lengths are shown in red, and dimensions of IDR-40, 78, and 156 are shown in shades of blue and gray. The red dashed line is an analytical fit with a scaling value of 0.80 with a prefactor value of 1.14. c Phase diagram of PopZ expressed in U2OS cells. (top) Three states of PopZ condensation: dilute phase (blue, left), two-phase (a diffused phase and condensed phase, red, middle), and a dense phase (gray, right). EGFP fluorescence intensity from blue (low) to white (high) and nucleus boundary as a white dotted line. Scale bar, 10 μm. (bottom) Phase diagrams of EGFP fused to either of the three PopZ variants. Each dot represents data from a single cell, positioned on the x-axis as a function of the cell mean cytoplasmic intensity. Dot color indicates phase. d Quantification of the partition coefficient of each of the three linkers. A higher partition coefficient indicates denser condensates. Two-sided student’s t-test; Four (two) asterisks indicate p-value < 0.0001 (0.01). n equals 30 granules per condition. Source data underlying graphs are provided in Source Data. e Schematics of the oligomerization domain (OD) of the wildtype PopZ (trivalent, left) and an OD with increased valency consisting of five helices, with a repeat of helices 3 and 4 (pentavalent, right). f The balance between condensation promoting and counteracting phase separation tunes condensate material properties. FRAP, shown as mobile fractions, for PopZ with a trivalent OD and a linker of three different lengths (gray and blue), and PopZ with a pentavalent OD with IDR-78 (light green) and IDR-156 (dark green). Two-sided student’s t-test; ****p-value < 0.0001. n equals 25 granules for each mutant. Source data underlying graphs are provided in Source Data.
