Solution-state NMR assignment and secondary structure analysis of the monomeric Pseudomonas biofilm-forming functional amyloid accessory protein FapA

FapA is an accessory protein within the biofilm forming functional bacterial amyloid related fap-operon in Pseudomonas, and maybe a chaperone for FapC controlling its fibrillization. To allow further structural analysis, here we present a complete sequential assignment of ¹H_amide, ¹³C_α, ¹³C_β, and ¹⁵N NMR resonances for the functional form of the monomeric soluble FapA protein, comprising amino acids between 29 and 152. From these observed chemical shifts, the secondary structure propensities (SSPs) were determined. FapA predominantly adopts a random coil conformation, however, we also identified small propensities for α-helical and β-strand conformations. Notably, these observed SSPs are smaller compared to the ones we recently observed for the monomeric soluble FapC protein. These NMR results provide valuable insights into the activity of FapA in functional amyloid formation and regulation, that will also aid developing strategies targeting amyloid formation within biofilms and addressing chronic infections.