Structural Basis for the Function of the β-Barrel Assembly-Enhancing Protease BepA

Area of Science:

• Structural Biology
• Molecular Biology
• Protein Biochemistry

Background:

• The β-barrel assembly machinery (BAM) complex is crucial for assembling β-barrel membrane proteins in the outer membrane.
• BepA (formerly YfgC) is a protease/chaperone that interacts with the BAM complex, influencing β-barrel protein assembly and degradation.

Purpose of the Study:

• To determine the full-length three-dimensional structure of BepA to understand its dual protease/chaperone functions.
• To elucidate the molecular mechanism underlying BepA's role in β-barrel membrane protein biogenesis.

Main Methods:

• X-ray crystallography was employed to determine the full-length BepA structure at 2.6-Å resolution.
• Structure-guided introduction of disulfide bonds was used to assess domain interactions and their role in BepA activity.

Main Results:

• The crystal structure revealed BepA comprises an N-terminal protease domain and a C-terminal tetratricopeptide repeat (TPR) domain that interact.
• In vivo functional assays showed that domain cross-linking did not alter BepA's activities, indicating no significant domain rearrangement is required for function.
• The determined structure is consistent with existing models of BepA's TPR domain docking with the BAM complex.

Conclusions:

• The solved structure provides a molecular basis for understanding BepA's function as a protease/chaperone in conjunction with the BAM complex.
• BepA's functional mechanism likely does not involve large-scale domain movements, supporting a static interaction model with the BAM complex.