Multiple driving forces required for efficient secretion of autotransporter virulence proteins

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Autotransporter (AT) proteins are crucial virulence factors in Gram-negative bacteria.
• Their translocation across the bacterial outer membrane (OM) is essential for function but lacks a defined energy source.
• Existing models do not fully explain the driving forces behind AT outer membrane transport.

Purpose of the Study:

• To quantitatively compare proposed mechanisms of AT protein translocation across the OM.
• To elucidate the role of passenger protein folding in the energy dynamics of AT secretion.
• To identify the energy source(s) driving AT outer membrane protein transport.

Main Methods:

• Utilized a combination of computational modeling and experimental techniques.
• Investigated the conformational state of AT passengers when translocation was inhibited.
• Analyzed the kinetics of AT secretion in relation to passenger folding.

Main Results:

• Demonstrated that blocked AT translocation results in an unfolded passenger protein in the periplasm.
• Established that AT secretion is a non-equilibrium process controlled by kinetics.
• Showed that passenger protein folding is coupled to the secretion process.

Conclusions:

• Proposed a model linking passenger protein conformation to the kinetics of AT secretion.
• Reconciled conflicting data on the role of passenger folding in AT OM translocation.
• Concluded that while passenger folding is involved, an additional energy source is necessary to initiate AT translocation.