Activation and secretion of Serratia hemolysin

Area of Science:

• Microbiology and Molecular Biology
• Bacterial Pathogenesis
• Protein Secretion Systems

Background:

• Serratia marcescens hemolysin (ShlA) is a pore-forming toxin secreted into the extracellular environment.
• ShlA is synthesized as an inactive precursor requiring processing for hemolytic activity.
• Secretion and activation are dependent on the outer membrane protein ShlB.

Purpose of the Study:

• To elucidate the mechanism of ShlA secretion and activation by ShlB.
• To identify the regions of ShlA responsible for secretion and pore formation.
• To investigate the role of ShlB in the post-translational modification of ShlA.

Main Methods:

• Analysis of ShlA secretion and activity in the presence and absence of ShlB.
• In vitro activation assays using cell lysates containing ShlB.
• Characterization of ShlA fragments to determine their role in secretion and activation.
• Comparative analysis with the HpmA hemolysin of Proteus mirabilis.

Main Results:

• ShlA remains inactive in the periplasm (ShlA*) without ShlB, exhibiting minimal hemolytic activity.
• ShlB mediates the secretion of ShlA and its conversion to the active hemolytic form.
• The N-terminal region of ShlA contains the signal for secretion and membrane insertion.
• ShlB or ShlA fragments can activate ShlA*, with fragments binding to direct ShlA* to the erythrocyte membrane.

Conclusions:

• ShlB is essential for the outer membrane translocation and activation of ShlA.
• The N-terminus of ShlA harbors critical domains for secretion, membrane targeting, and pore formation.
• A common activation mechanism involving ShlB and N-terminal fragments exists between ShlA and HpmA.