Signal peptide of FadA adhesin from Fusobacterium nucleatum plays a novel structural role by modulating the filament’s length and width

FadA, a novel adhesin of periodontal pathogen Fusobacterium nucleatum is composed of two forms, pre-FadA and mature FadA (mFadA), constituting the functional FadA complex (FadAc). By electron microscopy, we observed that mFadA formed uniformly long and thin filaments, while FadAc formed heterogeneous filaments of varying lengths and widths, as well as “knots”. Mutants in signal peptide or in the non-alpha-helical loop retaining heterogeneous structures had binding activity while those forming aggregates or long filaments lost activity. These observations suggest short filaments and knots may be the active forms of FadA. This is the first demonstration that a signal peptide is required for the assembly of a bacterial adhesin.Structured summary of protein interactionsmFadA and pre-FadAinteraction by transmission electron microscopy (View interaction)

► mFadA forms uniformly long and thin filaments with no binding activity.
► FadAc forms heterogeneous structures, due to the presence of pre-FadA.
► Heterogeneity of the FadA structure correlates with function.
► Shorter filaments may be the active form of FadA.
► First demonstration that signal peptide involved in adhesin assembly.