The membrane anchor of penicillin-binding protein PBP2a from Streptococcus pneumoniae influences peptidoglycan chain length

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Streptococcus pneumoniae is a significant Gram-positive pathogen with increasing antibiotic resistance.
• Beta-lactam antibiotics target peptidoglycan assembly, a key process in bacterial cell-wall synthesis.
• Understanding cell-wall synthesis is vital for developing strategies against drug-resistant bacteria.

Purpose of the Study:

• To characterize the glycosyltransferase activity of penicillin-binding protein (PBP)2a from Streptococcus pneumoniae.
• To investigate the role of different protein domains in PBP2a activity.
• To lay the groundwork for in vitro reconstitution of pneumococcal cell-wall assembly.

Main Methods:

• Purification of recombinant full-length membrane-anchored PBP2a using ion-exchange chromatography.
• Characterization of glycosyltransferase activity comparing full-length and truncated PBP2a forms.
• Assessment of transpeptidase activity through reactivity with bocillin and hydrolysis of a thiol-ester substrate analogue.

Main Results:

• The full-length PBP2a, including its cytoplasmic and transmembrane segments, synthesized longer glycan chains compared to a truncated periplasmic form.
• The transpeptidase active site of PBP2a demonstrated reactivity with bocillin and catalyzed thiol-ester hydrolysis.
• PBP2a failed to cross-link glycan chains in vitro, suggesting a missing component in the experimental system.

Conclusions:

• The glycosyltransferase activity of PBP2a is influenced by its full-length structure, including membrane-anchoring domains.
• While the transpeptidase active site is functional, its cross-linking activity is absent in vitro, indicating the need for additional factors.
• This study provides essential insights into PBP2a function for future in vitro reconstitution of pneumococcal cell-wall assembly.