Extended Data Fig. 5: Identification of FAP78 as the distal protrusion (DP) of the C. reinhardtii axoneme.
From: Axonemal structures reveal mechanoregulatory and disease mechanisms
a, Domain architecture of FAP78. FAP78 contains 16 armadillo (ARM) repeats interrupted with a helical/unstructured region. The C-terminal half contains a microtubule (MT) binding domain and an EF-hand like domain, which is not resolved in our cryo-EM map. b, Cryo-EM map of the DP colored by domain. c, Atomic model of FAP78. d, Sidechain density of a section of FAP78 boxed in panel c. e, The FAP78 model positioned within the subtomogram average of the C. reinhardtii axoneme (EMD-6872)24. The height of the DP is 155 Å in this map. FAP78 is located within 3–5 nm of IDAf and ODA4, suggesting a possible role in dynein regulation, although we do not observe direct interactions. f, The DP is absent from axonemes from human respiratory cilia (EMD-5950)32. The expected location is denoted by a dashed oval. The subtomogram averages in panels e and f are colored according to the color scheme established in Fig. 1. g, Phylogenetic distribution of FAP78 is limited to green algae and other single-celled ciliates. The homolog in T. thermophila only aligns to the C-terminal half of FAP78 and does not contain ARM repeats, which likely explains why a distal protrusion is not observed in subtomogram averages of T. thermophila axonemes (EMD-12119)84.
