Fig. 3: The medial disk is a lattice of PflC and PflD that interacts with the basal and proximal disks. | Nature Microbiology

Fig. 3: The medial disk is a lattice of PflC and PflD that interacts with the basal and proximal disks.

From: In situ structure of a bacterial flagellar motor at subnanometre resolution reveals adaptations for increased torque

Fig. 3

a, Asymmetric unit of the periplasmic scaffold highlighting the medial disk. Dashed box regions are enlarged in c, d and f. b, Comparing the WT subtomogram average motor structure (100 × 100 nm cross-section of EMD-3150 (ref. 17)) to a pflC deletion (100 × 100 nm cross-section, deposited as EMD-17415) reveals loss of the medial disk (open arrowhead; filled on WT structure), while pflD deletion (deposited as EMD-17416) abolishes assembly of a peripheral post-like density (open arrowhead; filled on WT structure). c, Close-up below the innermost basal disk ring shows a ring of 17 domain-swapped PflC protomers attached to FlgP trimeric repeats. A single PflC (dashed outline) contributes domains to 2 protomeric units. Asterisks denote the interdomain linker. d, View of the medial disk from outside the cell depicting 17 asymmetric units (dashed box highlights 1 asymmetric unit) of 7 PflC protomers and 1 PflD. PflC1 in pink; PflC2,4,6 in teal; PflC3,5 in cyan; PflC7 in blue. Inset: differential oligomerization interfaces of PflC protomers. Twofold symmetry axis symbols highlight symmetric dimerization; empty circles represent asymmetric interfaces. See focus in f. e, PflC and PflD interact with known flagellar components. Top: western blot of coIP of PflC-3×FLAG. Detected heavy (HC) and light (LC) antibody chains are indicated. C, culture; L, lysate. Middle: western blot of coIP of PflA-3×FLAG, PflD-sfGFP double-tagged strain. Sn1/2, supernatant 1/2; W, wash; E, eluate. Bottom: western blot of coIP of PflB-3×FLAG, PflD-sfGFP double-tagged strain. f, Top: molecular model of the PflC lattice denoting symmetry elements, enlarged from red box in d. Densities adjacent to every Asn239 denoted by asterisks correspond to a glycosylation site of PflC from a related species. Symmetry elements as in d. Bottom: side view of PflD beneath PflC4,5. g, The predicted structure of PflC (top) highlights common fold with HtrA (bottom), a periplasmic protease (PDB 6Z05 (ref. 36)). Left panel aligned to PflC1 in c. Protease and 2 PDZ domains labelled for comparison. See Extended Data Figs. 6 and 7 for further analysis.

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