1.X.  Intra-flagellar/Intra-ciliary Transport (If/IcT) Family 

Intraflagellar transport (IFT) is the highly conserved process by which proteins are transported along ciliary microtubules by a train-like polymeric assembly of IFT-A and IFT-B complexes. IFT-A is sandwiched between IFT-B and the ciliary membrane, consistent with its putative role in transporting transmembrane and membrane-associated cargoes. Meleppattu et al. 2022 used single-particle analysis cryo-EM to determine structures of native IFT-A complexes. They showed that subcomplex rearrangements enable IFT-A to polymerize laterally on anterograde IFT trains, revealing a cooperative assembly mechanism.  Binding of IFT-A to IFT-B shields the preferred lipid-binding interface from the ciliary membrane but orients an interconnected network of beta-propeller domains with the capacity to accommodate diverse cargoes toward the ciliary membrane. This provides a mechanistic basis for understanding IFT-train assembly and cargo interactions.