Structural divergence of paralogous S components from ECF-type ABC transporters

Area of Science:

• Structural biology
• Molecular microbiology
• Biochemistry

Background:

• Energy coupling factor (ECF) proteins are ATP-binding cassette transporters crucial for prokaryotic micronutrient uptake.
• ECF transporters comprise nucleotide-binding subunits, the ECF module (including EcfT), and a substrate-specific S component.

Purpose of the Study:

• To determine the high-resolution crystal structure of the biotin-specific S component, BioY, from Lactococcus lactis.
• To elucidate the structural basis for how diverse S components interact with a common ECF module while binding different substrates.

Main Methods:

• High-resolution (2.1 Å) X-ray crystallography of the BioY protein.
• Structural comparison with the thiamin-specific S component, ThiT, using root-mean-square deviation (RMSD).
• Analysis of BioY's substrate-binding properties in detergent solution.

Main Results:

• The crystal structure of BioY revealed significant structural differences compared to ThiT (RMSD = 5.1 Å), despite their shared function.
• A conserved N-terminal domain in S components mediates interaction with the ECF module.
• A divergent C-terminal domain is responsible for specific substrate binding, explaining functional versatility.
• Solitary BioY binds D-biotin with high affinity but does not exhibit transport activity.

Conclusions:

• The domain organization of S components allows for adaptation to various substrates while maintaining interaction with the ECF module.
• BioY's structure provides insights into the molecular mechanisms of ECF-mediated nutrient transport.
• Understanding these structures is key to comprehending micronutrient import pathways in prokaryotes.