Fig. 1

Structure and Localization of Tektins. a Schematic of the general structure of Tektin proteins consisting of two N-terminal alpha-helices (Helix 1A and Helix 1B) and a pair of C-terminal alpha-helices (Helix 2A and Helix 2B), separated by linker regions. Conserved amino acid motifs identified by Amos [20] are shown above. Conserved amino acid motifs identified in this study indicate similar motifs in the linker regions between the A and B helices of both alpha-helix pairs (black letters) as well as at the C-terminus of both B helices (red letters) are shown below. b Phylogenetic tree of metazoans and choanoflagellates indicating the evolutionary positions of the major phyla and key species examined in this study. c Location and composition of Tektin filaments within the axoneme of a motile cilium as proposed by Linck et al. [24]. The lower scheme shows a transverse section of the axoneme with the typical 9 plus 2 arrangements of 9 pairs of complete and incomplete microtubules (A in red, and B in blue, respectively) surrounding a central pair of A microtubules. Outer (yellow) and inner (red) dynein motor complexes, as well as radial spokes (blue) originating from each A microtubule are shown. The upper scheme details one doublet microtubule showing the thirteen and ten tubulin protofilaments that constitute the A- and B-microtubule, respectively, and the proposed localization of the Tektin filament (green sphere). Tektin filaments are thought to run along the inside of the A microtubule in each microtubule doublet of the axoneme. Tektin filaments are thought to be composed of multiples of three protein dimers: two Tektin-A/Tektin-B (Tektin-4/Tektin-2) heterodimers (thin red A and blue B circles) and one Tektin-C (Tektin-1) homodimer (thin green C circles)