Structural basis for bacterial lipoprotein relocation by the transporter LolCDE.

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Lipoproteins are essential components of the Gram-negative bacterial outer membrane, playing roles in vital functions and multidrug resistance.
• The lipopolysaccharide (LPS) transport (Lol) pathway facilitates the movement of lipoproteins from the inner to the outer membrane.
• The precise mechanism of LolCDE-mediated lipoprotein transport across the inner membrane remains largely unknown.

Purpose of the Study:

• To elucidate the mechanism of lipoprotein transport mediated by the ATP-binding cassette transporter LolCDE.
• To determine the structures of Escherichia coli LolCDE in various functional states.
• To identify key residues and structural features involved in the lipoprotein transport cycle.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to obtain high-resolution structures of LolCDE.
• Structures were determined for apo, lipoprotein-bound, LolA-bound, ADP-bound, and AMP-PNP-bound states.
• Mutagenesis and in vivo viability assays were performed to validate structural findings and identify functional residues.

Main Results:

• High-resolution cryo-EM structures (3.2-3.8 Å) of E. coli LolCDE were obtained, covering the complete transport cycle.
• The structures reveal distinct conformational states of LolCDE during lipoprotein translocation.
• Mutagenesis studies identified critical residues essential for LolCDE function and lipoprotein transport.

Conclusions:

• The study provides unprecedented structural insights into the mechanism of outer-membrane lipoprotein sorting and transport.
• Understanding the Lol pathway's mechanism can inform strategies to combat multidrug resistance in Gram-negative bacteria.
• The identified functional residues and structural characteristics of LolCDE offer potential targets for novel therapeutic interventions.