Figure 5. TUBB3 amino acid substitutions and phenotype-genotype-function correlations.

(A) Schematic of the TUBB3 protein; arrows indicate the location of each TUBB3 amino acid substitution. (B) Structure of the αβ-tubulin heterodimer from a rotated side view (pdb: 1JFF). α-tubulin is dark-shaded on right, and the arrows on the left point to each mutant residue, depicted in black, on β-tubulin. (C) Outside view of β-tubulin depicting each mutant residue in black with the exception of R62Q, which cannot be seen. The area proposed for motor protein interactions is depicted as a shaded grey oval. Residues R380, E410 and D417 are found in helices H11 and H12, respectively, on the external surface of β-tubulin. R262, found in the loop between helix H8 and strand 7, and A302, found in the loop following helix H9, are positioned laterally and below to helices H12 and H11, respectively. (D) Side interior view of β-tubulin showing the location of each mutant residue in black, with the exception of R380C, which is occluded by D417. R62 is positioned in the H1-S2 loop (N-loop) that forms lateral contacts with the M-loop of adjacent protofilaments. (E, top) Magnified image of β-tubulin depicting the putative hydrogen bond between the arginine side chain of R262 and the carbonyl oxygen of D417, both of which are shown in a stick representation. (E, middle and bottom) Both the R262C and R262H substitutions are predicted to break the hydrogen bond. (F) Phenotype-genotype and summary of functional data. AA = amino acid substitution; # ped = number of pedigrees; # aff = number of affected individuals; AC = anterior commissure hypoplasia; CC = corpus callosum hypoplasia; BG = basal ganglia dysgenesis; DD = developmental delay; FW = facial weakness; PN = progressive axonal sensorimotor polyneuropathy; CJC = congenital joint contractures; HD = heterodimer formation; HeLa = HeLa cell incorporation; MT dyn = microtubule dynamics (HS = highly stable, S = stable); Kip3p/2p = Kip3p and Kip2p microtubule plus-end accumulation ( ↓ decreased, ↑ increased). + denotes present; - denotes absent; −/+ denotes that only a subset of subjects have the feature and/or the findings are mild; variable (−) denotes rare participants with the substitution without CFEOM3.