Distinct core minor pilin complexes prime specialized type IV filaments in cyanobacteria.

Structural phylogenomics across 90 cyanobacterial genomes identifies two distinct core minor pilin priming complexes that initiate assembly of two morphologically distinct Type IV pilus filaments in Synechocystis sp. PCC 6803.

• Why it matters: Cyanobacteria encode many uncharacterized minor pilins, but their systematic roles in building specialized Type IV pilus filaments for different behaviors remain unclear.
• What they did: The study classified cyanobacterial pilins into six conserved families forming two putative core priming complexes, then used structural analysis and proteomic data to link PilX subunits and PilX2 to filament assembly and sensing.
• The result: The complexes prime short, hyper-dynamic competence pili and long, adhesive motility/phototaxis pili; a conserved beta-solenoid domain in PilX subunits is proposed to cap PilY1 homologs, and PilX2 facilitates motility pili assembly linked to DnaJ3 levels and cAMP-dependent surface sensing.