Conserved Omp85 lid-lock structure and substrate recognition in FhaC

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Omp85 proteins are essential for transporting polypeptides across and into cellular membranes.
• They possess a conserved architecture with POTRA domains, a β-barrel pore, and specific motifs involved in substrate interaction and translocation.
• Previous studies suggested conformational changes in the L6 loop play a role in Omp85 function.

Purpose of the Study:

• To elucidate the structural basis of Omp85 protein function, specifically focusing on the FhaC secretion protein.
• To investigate the role of conserved motifs and the L6 loop in the Omp85 mechanism.
• To understand the regulation of substrate binding in Omp85 proteins.

Main Methods:

• X-ray crystallography to determine the high-resolution structure of an FhaC variant.
• Reanalysis of existing Omp85 structural data.
• Comparative structural analysis to identify conserved features and conformational states.

Main Results:

• A 2.5 Å resolution structure of an FhaC variant revealed tightly interacting signature motifs forming a conserved 'lid lock'.
• Reanalysis confirmed that the L6 loop adopts a conserved resting state position across all known Omp85 structures.
• The structure identified a competitive mechanism for substrate binding regulation involving the linker to the N-terminal plug helix H1.

Conclusions:

• The conserved 'lid lock' and the resting state of the L6 loop are key features of Omp85 structure and function.
• Omp85-mediated translocation is regulated by a competitive mechanism involving the N-terminal plug helix H1 and its linker.
• This study refines our understanding of the Omp85 mechanism, highlighting conserved structural elements and regulatory strategies.