Structural Basis of Pseudomonas Biofilm-Forming Functional Amyloid FapC Formation

Biofilm-protected Pseudomonas aeruginosa causes chronic infections that are difficult to treat. FapC, the major biofilm forming functional-amyloid in Pseudomonas , is essential for biofilm integrity, yet its structural details remain unresolved. Using an integrative structural biology approach, we combine solution NMR-based structural ensemble of unfolded monomeric FapC, a ∼3.3 Å resolution CryoEM density map of FapC fibril, and all-atom MD simulations to capture transition from unfolded to folded monomer to fibrillar fold, providing a complete structural view of FapC biogenesis. CryoEM reveals a unique triple-layer β-solenoid cross-β fibril composed of a single protofilament. MD simulations initiated from monomeric and fibrillar FapC mapped structural transitions, offering mechanistic insights into amyloid assembly and disassembly. Understanding FapC reveals how Pseudomonas exploits functional amyloids for biofilm formation and establishes a structural and mechanistic foundation for developing therapeutics targeting biofilm-related infection and antimicrobial resistance.