Dynamic interplay between a TonB-dependent heme transporter and a TonB protein in a membrane environment

Area of Science:

• Microbiology and Structural Biology
• Computational Biophysics

Background:

• Gram-negative bacteria possess a complex cell envelope with inner and outer membranes, posing challenges for nutrient transport.
• Multicomponent protein systems, including TonB-dependent transporters (TBDTs), mediate the import of essential nutrients across these membranes.
• The precise molecular mechanisms and protein interactions within these systems remain poorly understood due to experimental limitations.

Purpose of the Study:

• To elucidate the dynamic molecular interactions between the outer membrane heme transporter HasR and the inner membrane protein HasB in *Escherichia coli*.
• To investigate the role of periplasmic domains in the complex formation and stability of this nutrient import system.
• To provide atomic-level insights into the energy transfer mechanism for heme internalization.

Main Methods:

• State-of-the-art molecular dynamics simulations of the *Escherichia coli* envelope model.
• Integration of computational simulations with experimental validation, including mutations, *in vivo* phenotypic assays, and biophysical methods.
• Analysis of protein-protein interactions within the periplasmic space.

Main Results:

• Revealed a previously unidentified network of protein-protein interactions between HasR and HasB in the periplasm.
• Demonstrated the critical role of periplasmic domains and their dynamics in the formation and stability of the HasR-HasB complex.
• Experimental validation confirmed the simulation-predicted interactions.

Conclusions:

• The study provides a dynamic, atomic-level view of heme import in Gram-negative bacteria.
• The identified interaction network is crucial for energy transfer and nutrient internalization.
• The findings are expected to apply to other nutrient import systems in bacteria, offering potential targets for new antibacterial strategies.