Fig. 1. PilY1 and minor pilins are essential for T4aP-dependent motility.
a Architectural model of T4aPM. The OM pore (PilQ secretin and TsaP) connect to PilP. PilP connect to a lower periplasmic ring (globular domains of PilN and PilO), which connect to a cytoplasmic ring (PilM)3. PilN/O and PilM generate a cage, which is occupied by PilC3. PilB and PilT associate with PilC in a mutually exclusive manner during extension and retraction, respectively3,68,69. For simplicity, PilB and PilT are not shown separately. Bent arrows, incorporation and removal from the pilus base of PilA during extension and retraction, respectively. Proteins labeled with single letters have the Pil prefix. b Schematic of M. xanthus gene clusters encoding PilY1 and minor pilins. Numbers below genes, distances between genes. Black lines below, genes deleted in cluster deletion mutants. c PilY1 and minor pilins are essential for T4aP-dependent motility. Scale bar, 1 mm. Strains motile by T4aP generate flares at the colony edge while strains non-motile by T4aP generate smooth-edged colonies. d Minor pilins and PilY1 are essential for T4aP formation. T4aP sheared off from ~15 mg cells were separated by SDS-PAGE and probed with α-PilA antibodies (top rows). Middle row, 40 µg of protein from total cell extracts were separated by SDS-PAGE and probed with α-PilA antibodies (middle rows) and, after stripping, with α-LonD antibodies as a loading control (bottom rows). e Minor pilins and PilY1 are essential for T4aP extension. Samples were prepared as in d. For better comparison, only 5% of T4aP sheared from the hyper-piliated ∆pilT strain (asterisk) and 25% of protein (hash) was applied. f Accumulation levels of T4aPM proteins. Protein from 3 × 108 cells was loaded per lane. In lane labeled ∆, protein from relevant in-frame deletion mutants was loaded. Gaps between lanes indicate lanes that were deleted for presentation purposes. g Bipolar localization of mCherry-PilM as a read-out for assembly of T4aPM. Scale bar, 5 µm. The results for the deletions of fimUpilVpilW en bloc in c–e were previously published3 and are included for comparison.