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