Architectures of Lipid Transport Systems for the Bacterial Outer Membrane

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Phospholipid transport between bacterial inner and outer membranes across the periplasm remains poorly understood.
• The role of the mammalian cell entry (MCE) protein family in this process is unclear.

Purpose of the Study:

• To elucidate the mechanisms and structures involved in phospholipid trafficking between bacterial membranes.
• To investigate the role of MCE proteins in mediating lipid transport.

Main Methods:

• Determining the structures of MCE proteins using electron microscopy (EM).
• Analyzing the assembly and function of MCE protein complexes in lipid transport.

Main Results:

• MCE proteins form hexameric assemblies with channels capable of lipid transport.
• E. coli MCE proteins MlaD, YebT, and PqiB exhibit diverse architectures: MlaD forms a ring with an ABC transporter, YebT forms a stacked ring tube, and PqiB forms a syringe-like structure.
• YebT and PqiB channels are long enough to span the periplasmic space, facilitating inter-membrane lipid transfer.

Conclusions:

• The MCE protein family utilizes diverse protein-based channel architectures for lipid transport between bacterial membranes.
• These findings reveal novel mechanisms for lipid trafficking in bacteria and potentially in eukaryotic organelles.