Fig. 3: The tubulin folding nucleus State 0.5.
From: Visualizing dynamic tubulin folding in chaperonin TRiC from nonnative nucleus to final native state
A The sliced side view of TRiC (in gray color) with one ring encapsulating tubulin density (in orange color) and the opposite ring in the apo state. B The tubulin density segmented from the map in A is displayed (in orange color) in the TRiC chamber of CCTs 1, 3, 6, 8, 7. C The native tubulin model (7TUB) is fit into the tubulin density in orange color, highlighting the tubulin E hook density at positively charged CCTs 1/4 pocket. Surface representations of TRiC subunits are colored by their electrostatic potential. D Top right: Three layers (segregated by two diagonal dotted lines) of bulky density in State 0.5 (in orange color) is the typical Rossman fold with a β sheet (lower left panel) sandwiched by two layers of alpha helices (upper left and lower right panel). Note: The native tubulin model is used only to illustrate the three layers of Rossman fold; registration is uncertain for the individual loosely formed β-strands. The view angle for each of three layers is as illustrated. E The topology diagram of tubulin highlighting the loosely folded secondary structure elements (highlighted in dark cyan) of State 0.5. The CCT residues participating in the salt bridge and hydrogen bond interactions with native tubulin are colored as the CCTs. The individual domains of tubulin are colored as in Fig. 1A. Background adapted from Cell 185, 4770–4787.e20 (2022), © Elsevier, used with permission. F i, ii, iii show the density in orange color of individual nonnative structure elements (in cyan color of N domain) that engage with CCT subunits and iv shows the absence of density for T3 loop in State 0.5, compared to that in State I (model in cornflower blue). The view angle for each of the four panels are illustrated in (G ii). G i shows the loosely assembled sequence of the folding nucleus (in orange) as part of the N domain (in cyan). ii shows the sites of the folding nucleus amino acid sequence (diamond) that engage with TRiC. iii shows the sequence of tubulin within the folding nucleus (in orange).
