Abstract
Purpose: The PBP4* is a Penicillin Binding Protein belonging to the class C of AmpH type whose function remains poorly understood. This study aimed to evaluate the biophysical and enzymatic properties of the Bacillus subtilis PBP4* to gain insights into its role in the context of bacterial cell wall recycling. Methods: To characterize the PBP4*, the full-length PBP4* and its N-terminal penicillin-binding domain have been produced in Escherichia coli and purified. Results: A comparison of biophysical properties has shown that both recombinant proteins are monomeric in solution and retain the same thermal stability. On the other hand, the D-alanine methyl esterase activity detected with the full-length PBP4* is impeded by the cleavage of the 92 amino acid C-terminal domain. The esterase activity of the full-length PBP4* strates a clear D-stereospecificity. The PBP4* is also active on B. subtilis cell walls bearing teichoic acids, compounds commonly substituted with D-alanine residues. Conclusions: Our results are in agreement with the hypothesis that PBP4* could play a role in recycling cell wall components, as previously suggested.
Highlights
The genome of Bacillus subtilis contains many genes coding for PenicillinBinding Proteins (PBPs) including pbpE which is translated into PBP4*, a protein of 451 amino acids (NCBI accession number: CCD10845)
This study aimed to evaluate the biophysical and enzymatic properties of the Bacillus subtilis PBP4* to gain insights into its role in the context of bacterial cell wall recycling
The results of Dynamic Light Scattering experiments performed on PBP4* and PBP4* ΔCTD have shown that both proteins are monomeric in solution, with estimated masses of 54.5 ± 1.22 and 35.17 ± 1.17 respectively (Figure 1(c))
Summary
The genome of Bacillus subtilis contains many genes coding for PenicillinBinding Proteins (PBPs) including pbpE which is translated into PBP4*, a protein of 451 amino acids (NCBI accession number: CCD10845). The PBP4* belongs to the class C of AmpH type and its function and cellular role remain poorly understood This PBP is composed of a N-terminal domain which har-. The N-terminal sequence of an apparent 56 kDa protein was identified as the beginning of the pbpE ORF, indicating that its product, named PBP4*, is not processed. This observation is in agreement with the absence of a predicted signal peptide in the PBP4* sequence. The authors conducted D-aminopeptidase activity assays with D-alanine-p-nitroanilide substrate but obtained negative results They proposed a role for PBP4* and RacX in the recycling of peptidoglycan components, a process especially important under starvation conditions [1]
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