Fig. 7
Sequence and structure conservation among DCX domains of TgDCX orthologues. a Sequences of DCX domains from Toxoplasma gondii, Vitrella brassicaformis, Chromera velia, Trichoplax adhaerens, N- and C-terminal domains of humans doublecortin, and a consensus DCX domain from the NCBI Conserved Domain Database (CD01617), were aligned using the MUSCLE program accessed through JalView (V2.10.5, http://www.jalview.org) with default parameters and displayed colored by polarity. Yellow: non-polar (G, A, V, L, I, F, W, M, P); Green: polar, uncharged (S, T, C, Y, N, Q); Red: polar, acidic (D, E); Blue: polar, basic (K, R, H). Secondary structure elements in TgDCX (beta sheet, “β”; alpha helix, “α”; turns, “T”; and a short stretch of 310 helix), derived from our X-ray crystal structure (PDB 6B4A) of TgDCX148–243, are indicated above the alignment. Black arrowheads indicate residues discussed in the text (TgDCX R152 and HsDCX-N K53; TgDCX D201). CvDCX1 (EupathDB ID: Cvel_6797), CvDCX2 (EupathDB ID: Cvel_18664), CvDCX3 (EupathDB ID: Cvel_28653), VbDCX1 (EupathDB ID: Vbra_15441), VbDCX2 (EupathDB ID: Vbra_12284), VbDCX3 (EupathDB ID: Vbra21191), PfDCX (EupathDB ID: PF3D7_0517800), TaDCX (Uniprot ID: B3RTF1) and HsDCX (NG_011750). b Superposition of backbone ribbon traces of TgDCX148–243 (dark gray-green; X-ray, 6B4A) on the N-terminal DCX domain of human doublecortin (yellow-orange; solution NMR, 1MJD) docked with the structure of αβ-tubulin (α-tubulin blue, β-tubulin cyan; electron crystallography, 1JFF) onto the cryoEM map of human doublecortin bound to microtubules (4ATU). The DCX domain binds in the groove between protofilaments, making contacts with two αβ-dimers. Side-chains are shown for some of the surface-exposed residues. The view is from the outside of the microtubule, corresponding to Fig. 2c of [9]. The (+)-end of the microtubule is towards the top. c Backbone ribbon threading of apicortin orthologue sequences onto the superimposed experimentally-determined structures of human DCX-N docked on microtubules (4ATU) and TgDCX148–243 (6B4A). The view is from the outside of the microtubule. The structures are rotated 135 degrees clockwise relative to the orientation shown in b. The microtubule (+)-end points toward the bottom right corner of the diagram. Only the portion of one β-tubulin close to the DCX domain is included. Side chains are shown for the electronegative patch on β-tubulin, close to DCX, identified as contact region #3 on β-tubulin by [9]. Side-chains of the residues discussed in the text, K53 on HsDCX-N and R152 on TgDCX are also shown, pointing away from tubulin in these structures