Required for the polymorphic O-glycosylation of the serine-rich repeat protein Fap1. A stabilizing protein that is part of the accessory SecA2/SecY2 system specifically required to export Fap1, a serine-rich fimbrial adhesin encoded upstream in the same operon. The GtfA-GtfB (Gtf1-Gtf2 in this bacteria) complex adds GlcNAc from UDP-GlcNAc to Fap1, attaching the first sugar residue. Cannot use not UDP-Glc as substrate. Stabilizes the glycosylation activity of GtfA, causing it to partially localize to the cellular membrane where it is more protease resistant. Protein modification; protein glycosylation. Interacts with glycosyltransferase GtfA (Gtf2); probably forms a heterotetramer with 2 subunits each of GtfA and GtfB. Part of the accessory SecA2/SecY2 protein translocation apparatus. No glycosylation of serine-rich fimbrial adhesin Fap1. The unglycosylated version of Fap1 accumulates which is larger than the wild-type protein. In a deletion mutant, GtfA (Gtf1) is less stable in vivo, no longer associates with the cell membrane and has an increased protease susceptibility. Biofilm formation decreases. In a double gftA/gtfB (gtf1/gtf2) mutant, there is no further affect on glycosylation but biofilm formation is further decreased. Belongs to the GtfB family.