The phosphothreonine lyase activity of a bacterial type III effector family

Area of Science:

• Microbiology
• Cellular Biology
• Biochemistry

Background:

• Pathogenic bacteria employ type III secretion systems (T3SS) to inject effector proteins into host cells.
• These effectors manipulate host cell signaling pathways to facilitate infection.
• Mitogen-activated protein kinases (MAPKs) are crucial signaling molecules often targeted by bacterial pathogens.

Purpose of the Study:

• To investigate the mechanism by which the Shigella type III effector OspF inactivates mitogen-activated protein kinases (MAPKs).
• To characterize the enzymatic activity responsible for OspF-mediated MAPK inactivation.

Main Methods:

• In vitro assays to assess the enzymatic activity of OspF on MAPKs.
• Mass spectrometry to analyze modifications of MAPKs after OspF treatment.
• Comparison of OspF activity with other related effector proteins.

Main Results:

• Shigella OspF irreversibly inactivates MAPKs, including extracellular signal-regulated kinases 1 and 2 (Erk1/2), c-Jun N-terminal kinase, and p38.
• OspF specifically removes phosphate groups from phosphothreonine residues in the MAPK activation loop.
• Mass spectrometry confirmed a 98-dalton mass loss in p-Erk2, indicative of phosphothreonine cleavage.
• This novel enzymatic activity was termed phosphothreonine lyase and found to be conserved among OspF family members.

Conclusions:

• OspF functions as a phosphothreonine lyase, targeting MAPKs for inactivation.
• This enzymatic activity represents a novel mechanism for bacterial manipulation of host signaling pathways.
• The specificity for MAPKs suggests a targeted strategy by Shigella to subvert host defenses.