Extended Data Fig. 10 |. Potential chemical modulation of radial spokes.

a, Calmodulin binds the IQ motif of FAP253 at the base of RS1. Below, sequence of FAP253 residues 400-430 showing the presence of an IQ motif (emboldened with motif-defining residues boxed). b, Structural comparison of calmodulin bound to FAP253 with apo-calmodulin bound to an IQ motif from myosin V (PDB 2IX7)⁴². c, Structural comparison of calmodulin bound to FAP253 with Ca²⁺-calmodulin bound to an IQ motif from myosin 5a (PDB 4ZLK)⁴². d, The structure of RSP5 resembles an NADPH-dependent aldo-keto reductase domain (PDB 2WZM)⁷⁶. However, the NADPH binding site of RSP5 is absent and filled by two loops (residues 393-414 and 468-484 of RSP5). e, The N-terminal domain of FAP198 closely resembles heme-binding cytochrome b5 (PDB 3X34)⁷⁷. However, no heme is observed bound to FAP198, and the putative heme-binding site is occluded by a loop of FAP198 (residues 89-95). f, RSP12 structurally resembles cylophilin-type peptidyl-prolyl cis-trans isomerase (PDB 1AK4)⁷⁸. The putative substrate-binding site of RSP12 is occupied by a loop of FAP198 (residues 96-105), which positions a proline (P99) in the active site. g, Atomic model of the GAF domain from RSP2 superposed with the model of a cAMP-bound GAF domain (PDB 1YKD)⁷⁹. Unexplained density in the RSP2 GAF domain (pink, contoured at 0.01) is observed in the cAMP binding pocket, but the resolution is insufficient to assign it as a cyclic nucleotide. The cAMP ligand from PDB 1YKD is shown for comparison. h, Atomic model of RSP23 superposed with an active, ADP-bound nucleoside diphosphate kinase (NDK; PDB 4HR2). Many of the active site residues are conserved. Potential density for a bound nucleotide to RSP23 is observed in the on-doublet map of RS1 (purple, contoured at 0.017) but not in the isolated RS1 map. The ADP ligand from PDB 4HR2 is shown for comparison.