The lipopolysaccharide-transporter complex LptB 2 FG also displays adenylate kinase activity in vitro dependent on the binding partners LptC/LptA

• Published in: The Journal of biological chemistry 2021-12, Vol.297 (6), p.101313
• Main Authors: Baeta, Tiago, Giandoreggio-Barranco, Karine, Ayala, Isabel, Moura, Elisabete C C M, Sperandeo, Paola, Polissi, Alessandra, Simorre, Jean-Pierre, Laguri, Cedric
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Adenylate Kinase - metabolism; ATP-Binding Cassette Transporters - metabolism; Biological Transport; Carrier Proteins - metabolism; Escherichia coli - metabolism; Escherichia coli Proteins - metabolism; Lipopolysaccharides - metabolism; Membrane Proteins - metabolism; Models, Molecular
• ISSN: 1083-351X

Lipopolysaccharide (LPS) is an essential glycolipid that covers the surface of gram-negative bacteria. The transport of LPS involves a dedicated seven-protein transporter system called the lipopolysaccharide transport system (Lpt) machinery that physically spans the entire cell envelope. The LptB FG complex is an ABC transporter that hydrolyzes ATP to extract LPS from the inner membrane for transport to the outer membrane. Here, we extracted LptB FG directly from the inner membrane with its original lipid environment using styrene-maleic acid polymers. We found that styrene-maleic acid polymers-LptB FG in nanodiscs display not only ATPase activity but also a previously uncharacterized adenylate kinase (AK) activity, as it catalyzed phosphotransfer between two ADP molecules to generate ATP and AMP. The ATPase and AK activities of LptB FG were both stimulated by the interaction on the periplasmic side with the periplasmic LPS transport proteins LptC and LptA and inhibited by the presence of the LptC transmembrane helix. We determined that the isolated ATPase module (LptB) had weak AK activity in the absence of transmembrane proteins LptF and LptG, and one mutation in LptB that weakens its affinity for ADP led to AK activity similar to that of fully assembled complex. Thus, we conclude that LptB FG is capable of producing ATP from ADP, depending on the assembly of the Lpt bridge, and that this AK activity might be important to ensure efficient LPS transport in the fully assembled Lpt system.