Biology subjects

Welsh, M. A.

Publications and source records attributed to Welsh, M. A..

4 recordsLinked to original sources

bioRxiv2025

Direct Amide Bond Formation By A Spore Peptidoglycan Biosynthetic Enzyme

The cortex layer of the peptidoglycan cell wall surrounding bacterial spores contains a modified sugar, muramic-{delta}-lactam, that is essential for spore germination. Genetic evidence has linked the conserved enzyme SwsB to the muramic-{delta}-lactam biosynthetic pathway. SwsB belongs to a large family of metal-dependent deacetylases, but its function is unclear because a putative catalytic residue is mutated. We have used native cortex peptidoglycan substrates to show that SwsB acts not as a deacetylase but as a monofunctional muramic-{delta}-lactam cyclase, the first enzyme reported with this activity. SwsB is remarkable in that it catalyzes lactam synthesis by direct intramolecular condensation of a carboxylate and primary amine with no apparent requirement for chemical energy input. SwsB will accept a minimal peptidoglycan substrate and, surprisingly, does not require a metal ion cofactor for cyclase activity. Our results suggest an in vivo role for SwsB and lay the foundation for mechanistic and structural studies of an unusual enzyme.

biochemistry↗

bioRxiv2023

Reconstituting spore cortex peptidoglycan biosynthesis reveals a deacetylase that catalyzes transamidation

Some bacteria survive in nutrient-poor environments and resist killing by antimicrobials by forming spores. The cortex layer of the peptidoglycan cell wall that surrounds mature spores contains a unique modification, muramic-{delta}-lactam, that is essential for spore germination and outgrowth. Two proteins, the amidase CwlD and the deacetylase PdaA, are required for muramic-{delta}-lactam synthesis in cells, but their combined ability to generate muramic-{delta}-lactam has not been directly demonstrated. Here we report an in vitro reconstitution of cortex peptidoglycan biosynthesis, and we show that CwlD and PdaA together are sufficient for muramic-{delta}-lactam formation. Our method enables characterization of the individual reaction steps, and we show for the first time that PdaA has transamidase activity, catalyzing both the deacetylation of N-acetylmuramic acid and cyclization of the product to form muramic-{delta}-lactam. This activity is unique among peptidoglycan deacetylases and is notable because it may involve the direct ligation of a carboxylic acid with a primary amine. Our reconstitution products are nearly identical to the cortex peptidoglycan found in spores, and we expect that they will be useful substrates for future studies of enzymes that act on the spore cortex.

biochemistry↗

bioRxiv2018

FtsW is a peptidoglycan polymerase that is activated by its cognate penicillin-binding protein

The peptidoglycan cell wall is essential for the survival and shape maintenance ofbacteria.1 For decades it was thought that only penicillin-binding proteins (PBPs) effected peptidoglycan synthesis. Recently, it was shown that RodA, a member of the Rod complex involved in side wall peptidoglycan synthesis, acts as a peptidoglycan polymerase.2-4 RodA is absent or dispensable in many bacteria that contain a cell wall; however, all of these bacteria have a RodA homologue, FtsW, which is a core member of the divisome complex that is essential for septal cell wall assembly.5,6 FtsW was previously proposed flip the peptidoglycan precursor Lipid II to the peripasm,7,8 but we report here that FtsW polymerizes Lipid II. We show that FtsW polymerase activity depends on the presence of the class B PBP (bPBP) that it recruits to the septum. We also demonstrate that the polymerase activity of FtsW is required for its function in vivo. Our findings establish FtsW as a peptidoglycan polymerase that works with its cognate bPBP to produce septal peptidoglycan during cell division.

microbiology↗

bioRxiv2018

Maturing Mycobacterial Peptidoglycan Required Non-canonical Crosslinks to Maintain Shape

In most well studied rod-shaped bacteria, peptidoglycan is primarily crosslinked by penicillin binding proteins (PBPs). However, in mycobacteria, L,D-transpeptidase (LDT)-mediated crosslinks are highly abundant. To elucidate the role of these unusual crosslinks, we characterized mycobacterial cells lacking all LDTs. We find that LDT-mediated crosslinks are required for rod shape maintenance specifically at sites of aging cell wall, a byproduct of polar elongation. Asymmetric polar growth leads to a non-uniform distribution of these two types of crosslinks in a single cell. Consequently, in the absence of LDT-mediated crosslinks, PBP-catalyzed crosslinks become more important. Because of this, Mycobacterium tuberculosis (Mtb) is more rapidly killed using a combination of drugs capable of PBP- and LDT-inhibition. Thus, knowledge about the single-cell distribution of drug targets can be exploited to more effectively treat this pathogen.

microbiology↗