Tip subunit of the minor fimbriae. These filamentous pili are attached to the cell surface; they mediate biofilm formation, adhesion onto host cells and onto other bacteria that are part of the oral microbiome (PubMed:24118823, PubMed:26001707). They play an important role in invasion of periodontal tissues and are recognized as major virulence factors. Fimbrium subunits from different strains have highly divergent sequences, and this correlates with pathogenicity (Probable). Component of the fimbrium tip (PubMed:24118823). Minor fimbriae are composed of a structural subunit, most often Mfa1, and the accessory subunits Mfa3, Mfa4 and Mfa5 (PubMed:19589838, PubMed:24118823, PubMed:26001707). Fimbrium assembly occurs by linear, head-to-tail oligomerization of fimbrial subunits. This is mediated via insertion of a C-terminal beta-strand from one subunit into a groove in the N-terminal domain of the following subunit (Probable). Mfa3 is required for Mfa4 and Mfa5 insertion into the fimbrium (PubMed:24118823). Targeted to the outer membrane as a palmitoylated precursor. The lipid modification is no longer present after proteolytic processing to the mature form (PubMed:26437277). Detected at the tip of the fimbriae (PubMed:24118823). Mildly increased autoaggregation. The name (minor fimbrium subunit) does not indicate the abundance of the protein, but is derived from the greater length of the major fimbriae. In strain ATCC 33277 and strain ATCC BAA-1703 / FDC 381, major fimbriae are 300 - 1600 nM in length and about 5 nm in diameter. In contrast, minor fimbriae are only about 80 - 120 nm long. This length difference is observed only in a small number of strains, including strain ATCC 33277 and strain ATCC BAA-1703 / FDC 381, and is due to a loss of function mutation in FimB, a protein that restricts fimbrial length in other strains. Belongs to the bacteroidetes fimbrillin superfamily. FimB/Mfa2 family.