Role of penicillin binding proteins in synthesis and modification of bacterial cell envelope

Abstract

The bacterial cell wall is a critical structure that maintains cell integrity by preventing lysis due to internal osmotic pressure and defining cell shape. In Bacillus subtilis, the major components of the cell wall are peptidoglycan (PG) and teichoic acids (TAs). PG forms a net-like structure around the cytoplasmic membrane, with penicillin-binding proteins (PBPs) playing a central role in its synthesis by utilizing lipid II as a precursor. Most bacteria encode multiple PBPs, many of which are functionally redundant, allowing survival despite the loss of certain PBPs. PBPs have been key antibiotic targets for decades, particularly following the discovery of penicillin, leading to extensive research on their redundancy and functional roles. Understanding PBP redundancy in B. subtilis is essential for designing novel antibiotics that specifically target essential PBPs to combat antibiotic resistance. This thesis investigates PBP redundancy and functional specialization in B. subtilis by systematically deleting PBPs to determine which are essential for growth during the exponential phase. The findings reveal that PBP2a (PBPH) and PBP2b are the only essential PBPs required for maintaining bacterial viability. Further, structural manipulation of PBP2a and its redundant partner PBPH identified the transmembrane domain of PBPH as a key regulator of PBP2a transcription and functional redundancy. Additionally, this research characterizes the previously unstudied PBPX in B. subtilis. A bioinformatics-based structural analysis predicted its D-alanine transferase activity, which was subsequently confirmed experimentally. These findings expand our understanding of PBP functional diversity and may contribute to the development of new antibacterial strategies targeting cell wall biosynthesis in B. subtilis and related bacteria