Extended Data Fig. 8: PRKAR2A and CATIP are anchored in the RS3 stalk, but their functional domains are flexibly positioned.

a) Slice through the cryo-EM 3D reconstructed RS3 head-neck. Note the blurred and unresolved density on the proximal side of the neck region (ellipse), suggesting structural flexibility of subunit(s) in this region. b, c) AlpaFold2 model predictions of full length PRKAR2A and CATIP show both two high confidence regions (blue), that is, large functional domains that connect through flexible linkers to small helical segments (that is the N-terminal region of PRKAR2A and mid region of CATIP) that attach the proteins to the RS3 stalk by interacting with CFAP91 and each other. The model predictions are color-coded by ‘per-residue confidence score’ (pLDDT) from the highest (blue) to the lowest score (red). d, e) The unassigned, large globular domains of the AlphaFold2 predicted models of PRKAR2A and CATIP show reasonable fitting to the unresolved cryo-EM density in the RS3 neck region. (e) shows a zoom-in of the dash-circled area in (d). f, g) The atomic model of RS3 (as seen in Fig. 2) but including the full-length predicted models of PRKAR2A and CATIP. h, i) The long, disordered liker regions of CATIP (h) and PRKAR2A (i) could provide a large radius of gyration (symbolized as sphere) of the large globular domains around their stalk-anchored helical domains (maximum radius predicted based on number of amino acids in the linker x 3.5 Å). Scale bar: (a) 10 nm.