The membrane bound bacterial lipocalin Blc is a functional dimer with binding preference for lysophospholipids

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Lipocalins are small, multifunctional proteins found in eukaryotes and bacteria.
• Class I bacterial lipocalins are outer membrane lipoproteins, with E. coli's Blc being well-studied.
• Blc is expressed during starvation and high osmolarity, suggesting a role in cell envelope stress response.

Purpose of the Study:

• To investigate the lipid-binding properties of E. coli Blc.
• To elucidate the function of Blc in bacterial lipid metabolism and membrane maintenance.

Main Methods:

• Fluorescence quenching experiments to determine binding affinities.
• Crystallography to determine the structure of Blc bound to vaccenic acid.
• Analysis of Blc's binding site and its implications for ligand interaction.

Main Results:

• Dimeric Blc binds fatty acids and phospholipids with micromolar dissociation constants (K(d)).
• The crystal structure reveals a Blc dimer binding site opposite its membrane-anchored face.
• Blc exhibits nanomolar K(d) for lyso-phospholipids, indicating high-affinity binding.

Conclusions:

• Blc likely plays a role in the storage or transport of lipids essential for membrane integrity.
• The high-affinity binding of lyso-phospholipids suggests a specific function in their metabolism within the bacterial outer membrane.