Processing of the lactococcal extracellular serine proteinase

Area of Science:

• Microbiology
• Enzymology
• Protein Biochemistry

Background:

• The activity of lactococcal serine proteinase is linked to the membrane-associated lipoprotein PrtM.
• Understanding the roles of PrtM and the proteinase in maturation is crucial.

Purpose of the Study:

• To investigate the specific function of PrtM in lactococcal serine proteinase maturation.
• To differentiate the actions of PrtM from the proteinase itself.

Main Methods:

• Construction of an inactive lactococcal proteinase mutant by active site amino acid mutation.
• Comparison of secreted inactive proteinase forms with and without PrtM.
• Analysis of proteinase isolation under different genetic conditions (prtM absence, inactive active site).

Main Results:

• Inactive proteinases (mutant or PrtM-deficient) were larger than the active form.
• Absence of PrtM or a functional active site prevented proteinase isolation from cells.
• PrtM appears necessary for the correct processing and release of the active proteinase.

Conclusions:

• PrtM facilitates the autoproteolytic removal of the N-terminal pro-region of the serine proteinase.
• Further C-terminal autodigestion, dependent on PrtM, releases the active enzyme from lactococcal cells.