Fig. 4: Structural basis of PELP1 Rix1 domain interaction with WDR18.

a Schematic representation of WDR18 with WD repeat regions that contribute to β-propeller domain and features of the C-terminal tail noted below. b Schematic representation of PELP1’s Rix1 domain with localization of LxxLL and PxxP motifs. Specific motifs and features involved in PELP1-WDR18 interaction are noted below. c Side view of cryo-EM density showing interaction plane between dimerized PELP1 and WDR18. d Model zoom of WDR18 β-propeller domain loops extending into both protomers of PELP1. Viewpoint is from top of PELP dimer interface (LM11 in view). Parts of the model that are colored white represent residues involved in the PELP1-WDR18 interaction interface. Superscripts denote individual protomers. e Footprint representation of WDR18 interaction with both PELP1 protomers in the assembly, illustrated by white colored surface on PELP1. Cartoon representation of the 7 WDR18 β-propeller blades are color coordinated (light blue and teal) to exhibit individual blade contacts with specific PELP1 protomers. Brown coloration stands for no blade contact with PELP1. f Side view of cryo-EM density with half the assembly hidden for visualization of WDR18 C-terminal tail inside the hollow core. g Model zooms of WDR18 C-terminal tail interactions with inner surface of PELP1. Left panel illustrates small β-sheet interactions between β1 of PELP1 Rix1 domain and β28 of the WDR18 C-terminal tail as it descends into the hollow assembly core. Right panel illustrates a descending α-helix 3 of the WDR18 C-terminal tail interacting with three LxxLL motifs of the same PELP1 protomer (LM2-LM3-LM4). Parts of the model that are colored white represent residues involved in the PELP1-WDR18 interaction interface. LxxLL motifs colored in gold to represent roles in assembly inter-subunit bridging. Superscripts denote individual protomers. h N-terminal FLAG-tagged WDR18 wild type or C-terminal tail deleted mutant (1-344aa) constructs were used as bait for co-IP and assessed for full-length PELP1 binding. SDS-PAGE of eluted co-IP samples followed by total protein staining exhibited enrichment of C-terminally truncated PELP1 only with wild type WDR18 and not with C-terminal tail deleted WDR18 (lane 2 vs. 3). co-IP and Western blot experiments in (h) were performed at least two times with reproducible results.