LptALptG

LptALptG is a term used to describe the relationship between two components of the lipopolysaccharide transport (Lpt) system in Gram-negative bacteria: LptA, a periplasmic adaptor protein, and LptG, an inner membrane component of the LptB2FG transporter. The Lpt system ferries lipopolysaccharide (LPS) from its site of synthesis in the inner membrane to the outer membrane, where LPS is inserted into the outer membrane structure. LptA and LptG play distinct but complementary roles within this pathway.

LptA is a soluble periplasmic protein that forms part of a continuous, periplasmic “bridge” linking inner membrane components to the outer membrane assembly machinery. It is characterized by an elongated, flexible structure that enables interactions with multiple partners along the transport route, including LptC on the inner membrane side and LptD/E on the outer membrane side. Through these interactions, LptA helps shuttle LPS across the periplasm.

LptG is an integral inner membrane protein that partners with LptF as part of the LptB2FG transporter complex. This inner membrane complex uses energy derived from ATP hydrolysis to extract LPS from the inner membrane and initiate its transfer into the periplasmal bridge formed by LptA.

Together, LptA and LptG contribute to the coordinated movement of LPS across the periplasm to the outer membrane. The proper function of LptALptG is critical for outer membrane integrity and bacterial viability, and components of the Lpt system are considered potential targets for antimicrobial strategies.