DL-endopeptidases function as both cell wall hydrolases and poly-γ-glutamic acid hydrolases

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• Biopolymers on cell surfaces are crucial for microbial protection and nutrient storage.
• Poly-γ-glutamic acid (γ-PGA) is a significant biopolymer produced by Bacillus species.
• While γ-PGA synthesis is studied, its modification and degradation pathways are less understood.

Purpose of the Study:

• To investigate the γ-PGA degrading capabilities of Bacillus subtilis dl-endopeptidases.
• To compare the substrate specificity and regulation of γ-PGA hydrolysis by dl-endopeptidases and PgdS.

Main Methods:

• Enzymatic assays using purified dl-endopeptidases (LytE, LytF, CwlS, CwlO, CwlT) and PgdS.
• Analysis of γ-PGA digestion patterns with varying d-Glu:l-Glu ratios.
• Inhibition studies using IseA to assess enzyme regulation.

Main Results:

• Several dl-endopeptidases digest both peptidoglycan and γ-PGA linkages.
• PgdS exhibits restricted substrate specificity, hydrolyzing specific d-/l-Glu linkages in γ-PGA.
• dl-endopeptidases demonstrate broader substrate specificity, cleaving various d-/l-Glu linkages in γ-PGA.
• IseA inhibits dl-endopeptidases' activity on both peptidoglycans and γ-PGA, but not PgdS's γ-PGA hydrolysis.

Conclusions:

• Bacillus subtilis dl-endopeptidases possess significant, flexible γ-PGA hydrolase activity.
• These enzymes degrade γ-PGA more broadly compared to the specialized hydrolase PgdS.
• The findings expand the known functions of dl-endopeptidases beyond peptidoglycan degradation.