Responsible, at least in part, for generating a meso-diaminopimelyl-3-a meso-diaminopimelyl-3 cross-link. Cell wall biogenesis; peptidoglycan biosynthesis. Simultaneous disruption of erfK, ybiS, ycfS and ynhG leads to loss of a significant proportion of muropeptides, including those with meso-DAP-3-meso-DAP-3 cross-links and with covalently anchored major outer membrane lipoprotein (Lpp) to the peptidoglycan. Overexpression of ycbB in this background increases meso-diaminopimelyl-3-a meso-diaminopimelyl-3 cross-links but does not restore Lpp anchoring. Belongs to the YkuD family.