Required for the polymorphic O-glycosylation of the serine-rich repeat protein Srr2. A stabilizing protein that is part of the accessory SecA2/SecY2 system specifically required to export serine-rich repeat proteins, probably Srr2 in this organism. The GtfA-GtfB (Gtf1-Gtf2 in this bacteria) complex adds GlcNAc from UDP-GlcNAc to Srr2 substrate, attaching the first sugar residue. Stabilizes the glycosylation activity of GtfA in vivo. Upon expression in a gtfB deletion mutant of S.parasanguis, GtfB confers incorrect glycosylation and partial complementation of a biofilm formation defect, while GtfA/GtfB restores correct expression of serine-rich repeat protein Fap1 and completely restores a biofilm formation defect in a S.parasanguis double gtfA-gtfB deletion. Protein modification; protein glycosylation. Interacts with glycosyltransferase GtfA (Gtf1) (PubMed:21862581). Interacts with glycosyltransferase GtfA; 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 repeat protein Srr-2. Belongs to the GtfB family.