This subfamily consists of Escherichia coli AfaD, Salmonella SafD, and similar proteins. The afa gene clusters encode an afimbrial adhesive sheath produced by Escherichia coli. The adhesive sheath is composed of two proteins, AfaD and AfaE, which are independently exposed at the bacterial cell surface. AfaE is required for bacterial adhesion to HeLa cells and AfaD for the uptake of adherent bacteria into these cells. SafD is the minor subunit of Saf pili, which are often found in clinical isolates of Salmonella and are assembled by the chaperone-usher secretion pathway. In addition to safD, the saf operon is also composed of safA (major subunit), safB (periplasmic chaperone), and safC (outer membrane usher). Also included is the enteroaggregative Escherichia coli AAF/IV pilus tip protein, which is implicated in adhesion as well. During fimbria/pili assembly, polymerization occurs when the N-terminal extension (NTE) of one monomer is inserted into an adjacent monomer, providing the final beta strand or G-strand, to complete the Ig-like fold, in a mechanism called the donor-strand complementation (DSC) or donor-strand exchange (DSE).
Comment:During fimbria/pili assembly, polymerization occurs when the N-terminal extension (NTE) of one monomer is inserted into an adjacent monomer, providing the final beta strand or G-strand, to complete the Ig-like fold, in a mechanism called the donor-strand complementation (DSC) or donor-strand exchange (DSE).
Structure:5D55: Escherichia coli Hda pilus minor tip subunit, HdaB, forms domain-swapped homodimer, contacts at 4A
Jiyao W et al.(2023). "The conserved domain database in 2023.",