This is the C-terminal domain found in d-transpeptidases (Ldt) homologues from E.coli. Three of these enzymes (YbiS, ErfK, YcfS) have been shown to cross-link Braun's lipoprotein to the peptidoglycan (PG), while the other two (YnhG, YcbB) form direct meso-diaminopimelate (DAP-DAP, or 3-3) cross-links within the PG. Family members include erfK (ldtA), ybiS (ldtB), ycfS (ldtC), and ynhG (ldtE).

1: Phenotypic analysis of Eschericia coli mutants lacking L,D-transpeptidases. Sanders AN, Pavelka MS; Microbiology. 2013;159:1842-1852. PMID:23832002