Table 1.
Pilus system attributes for CU and SA pili
| CU assembled Pili | SA pili | |
|---|---|---|
| Fiber initiation | Tip adhesins with highest binding affinity for the usher are incorporated first | Major subunit sufficient to initiate fiber polymerization by the pilin sortase |
| Fiber organization | Tip adhesin Tip fibrillum Major subunit backbone |
Minor subunit tip in some SA pili Minor subunits interspersed Major subunit backbone |
| Fiber organization | Non-covalent interactions via DSE | Covalent inter- and intra-subunit peptide bonds |
| Fiber termination | Incorporation of minor pilin subunit that cannot undergo DSE | Incorporation of minor pilin subunit that is attached to the cell wall by the housekeeping sortase |
| Receptor interactions | Ligand interactive sites mapped to tip adhesin | Minor subunits mediate adhesion, molecular basis undetermined |
| Assembly platform | Usher–mediated, location not examined | Secretion and sortase enzymes spatially restricted |
| Pilus fiber display | Peritrichous | Focal assembly; peritrichous display and/or absent from septum after cell wall attachment |