D-Stereoisomer preference of the OmpA-like domain of Pal in peptidoglycan of Acinetobacter baumannii

OmpA-like domain proteins bind to peptidoglycan by interacting with the D-amino acid moiety of meso-diaminopimelate in peptidoglycan, but it is still not clear how this domain recognizes the D-amino region of peptidoglycan. To study their D-stereoisomer preference, we solved the crystal structures of the OmpA-like domains of Acinetobacter baumannii peptidoglycan-associated lipoprotein (AbPal) in complex with D- or L-diaminopimelate. Our results reveal that these domains can bind both enantiomers of diaminopimelate with a greater affinity for D-diaminopimelate. The crystal structures of wild-type AbPal in complex with meso-diaminopimelate and mutant AbPal in complete with the LL-diaminopimelate ligand suggests that the Tyr85 residue of AbPal is an important determinant for this D-amino acid moiety preference. Our findings provide a basis for the development of antibacterial agents that inhibit interactions between PGN and OmpA-like domains and disrupt the stability of cell walls of gram-negative bacteria.