Fig. 5: MD simulations reveal how phosphorylation modulates the strength of the FLNC_d24 homo- and heterodimer interfaces.

A The location of the T2677 and Y2683 phosphorylation sites on the FLNC_d24 homodimer (PDB 1V05) and FLNC_d24:HSPB7_ACD^C131S heterodimer structures is near the interface. FLNC: orange; HSPB7: purple. B Difference map of hydrogen bond occupancy between WT and either pT2677 (lower right triangle) or pY2683 FLNC_d24 (upper left) homodimers. Each pixel corresponds to a particular inter-monomer contact between residue pairs. Blue: hydrogen bond formed more in the phosphorylated form; red: hydrogen bond formed more in the WT. A highly occupied hydrogen bond formed across the WT homodimer interface (between E2681 and Y2683) is lost upon phosphorylation of Y2683 (WT 71%; pY2683 0%). And a new interaction with R2690 is formed upon phosphorylation of T2677 (WT 0%; pT2677 26%) (insets). C Difference maps of hydrogen bond occupancy between WT and pT2677 (upper) or pY2683 FLNC_d24:HSPB7_ACD^C131S heterodimers (lower). Colouring as in (B). The most substantial differences are highlighted with representative frames from the trajectories showing the contacts made (insets). These are: a highly occupied hydrogen bond formed across the WT heterodimer interface (between G2674 and N107) lost upon phosphorylation of T2677 (WT 63%; pT2677 1%); and a new interaction is formed between pY2683 with R113 that is absent in the WT (WT 0%; pY2683 32%). Altered interactions are also observed between residues that do not directly involve the phosphorylated site, e.g. a contact between D2712 and T143 (WT 10%; pT2677 38%) and ones between the cluster H2686/N2689/R2690 and E99 (WT 0/0/22%; pY2683 28/41/45%). For a full inventory of hydrogen bond occupancies, see the Supplementary Data 1.