Dynamic basis of lipopolysaccharide export by LptB₂FGC

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Gram-negative bacteria utilize lipopolysaccharides (LPS) for resistance, including antibiotic resistance.
• The lipopolysaccharide transport (LPT) complex, comprising seven proteins (LptA-G), is essential for exporting LPS across the bacterial envelope.
• The LptB2FG ATP-binding cassette transporter's mechanism for LPS transfer to LptC is not fully understood.

Purpose of the Study:

• To elucidate the mechanism by which LptB2FG couples ATP hydrolysis with LPS transport to LptC.
• To investigate the conformational dynamics of the LptB2FG and LptB2FGC complexes.
• To understand the regulation of LPS entry into the transport complex.

Main Methods:

• Pulsed dipolar electron spin resonance spectroscopy was employed to study conformational heterogeneity in micelles and proteoliposomes.
• Laser-induced liquid bead ion desorption mass spectrometry was used to monitor LPS binding and release.
• Analysis of protein-protein interactions and domain movements within the LPT complex.

Main Results:

• The LptF β-jellyroll domain maintains stable interactions with LptG and LptC β-jellyrolls.
• ATP binding allosterically controls the opening of the periplasmic LptF β-jellyroll domain and closes nucleotide-binding domains.
• LptC binding modulates the LPS entry gate's flexibility, revealing dynamic regulation of LPS transport.

Conclusions:

• The study reveals ATP-dependent allosteric gating of the LptF β-jellyroll domain, crucial for LPS transport.
• Regulation of the LPS entry gate by LptC's dynamic transmembrane helix ensures efficient and unidirectional LPS translocation.
• These findings provide insights into the intricate mechanism of LPS export in Gram-negative bacteria.