Together with LptE, is involved in the assembly of lipopolysaccharide (LPS) at the surface of the outer membrane. Contributes to n-hexane resistance. Component of the lipopolysaccharide transport and assembly complex. Interacts with LptE and LptA. May interact with LptE during assembly of LptD by the beta-barrel assembly machine. Constitutively expressed. Contains an N-terminal soluble domain that is likely periplasmic and interacts with LptA, and a C-terminal transmembrane domain, which is predicted to be a beta-barrel and interacts with LptE. Residues 529-538 play a key role in interaction with LptE. Contains two intramolecular disulfide bonds. At least one disulfide bond is required for activity, and protein is probably fully oxidized in vivo. Mutations alter the permeability of the outer membrane resulting in increased sensitivity to detergents, antibiotics and dyes. Depletion leads to filamentation followed by membrane rupture and cell lysis. The correct assembly of LptD depends on the thiol:disulfide interchange proteins DsbA and DsbC, the chaperone proteins SurA and Skp, LptE and the chaperone/protease BepA (PubMed:20566849, PubMed:20615876, PubMed:21257904, PubMed:21257909, PubMed:23772069, PubMed:24003122). Incorrectly folded LptD can be degraded by three different proteases, DegP, BepA and YcaL. These proteases act at distinct points in the outer membrane protein assembly (PubMed:24003122, PubMed:28784813). Belongs to the LptD family.