Proteolytic cleavage inactivates the Staphylococcus aureus lipoteichoic acid synthase

Area of Science:

• Microbiology
• Enzymology
• Cell Biology

Background:

• Lipoteichoic acid (LTA) is vital for Gram-positive bacterial cell envelopes.
• In Staphylococcus aureus, LTA synthesis is mediated by the membrane-bound LtaS enzyme, comprising N-terminal transmembrane helices (5TM) and an extracellular enzymatic domain (eLtaS).

Purpose of the Study:

• To elucidate the mechanism of LtaS enzyme processing and its functional implications in LTA synthesis.
• To identify the protease responsible for LtaS cleavage and investigate the role of its domains in enzyme activity.

Main Methods:

• Investigated LtaS processing using spsB depletion and site-directed mutagenesis.
• Assessed enzyme function by constructing hybrid proteins and expressing separate LtaS domains.
• Utilized biochemical assays to detect enzyme activity.

Main Results:

• SpsB was identified as the essential protease cleaving LtaS after residues 215Ala-Leu-Ala217.
• Inhibition of cleavage via proline substitution abolished LtaS processing.
• The 5TM domain is critical for LtaS function, and separate domains lack activity, indicating essential intra-molecular interactions.

Conclusions:

• Full-length LtaS is the only active form for LTA synthesis.
• Proteolytic cleavage by SpsB serves as an irreversible inactivation mechanism for the LtaS enzyme.
• Specific interactions between the 5TM and eLtaS domains are required for LtaS functionality.