LptB2FG is an ABC transporter with Adenylate Kinase activity regulated by LptC/A recruitment

Abstract

Lipopolysaccharide (LPS) is an essential glycolipid covering the surface of gram-negative bacteria. Its transport involves a dedicated 7 protein transporter system, the Lpt machinery, that physically spans the entire cell envelope. LptB2FG complex is an ABC transporter that hydrolyses Adenosine Triphosphate (ATP) to extract LPS from the inner membrane (IM). LptB2FG was extracted directly from IM with its original lipid environment by Styrene-Maleic acids polymers(SMA). SMA-LptB2FG in nanodiscs displays ATPase activity and a previously uncharacterized Adenylate Kinase (AK) activity. It catalyzes phosphotransfer between two ADP molecules to generate ATP and AMP. ATPase and AK activities of LptB2FG are both stimulated by the interaction on the periplasmic side with LptC and LptA partners and inhibited by the presence of LptC transmembrane helix. Isolated ATPase module (LptB) has weak AK activity in absence of LptF and LptG, and one mutation, that weakens affinity for ADP, has AK activity similar to that of fully assembled complex. LptB2FG is thus capable of producing ATP from ADP depending on the assembly of the Lpt bridge and the AK activity might be important to ensure efficient LPS transport in fully assembled Lpt system.