Karl Ocius

Molecules. 2021 Oct 21;26(21):6352. doi: 10.3390/molecules26216352.

ABSTRACT

Muramyl dipeptide (MDP) is the smallest peptidoglycan fragment able to trigger the immune response. Structural modification of MDP can lead to the preparation of analogs with improved immunostimulant properties, including desmuramyl peptides (DMPs). The aim of this work was to prepare the desmuramyl peptide (L-Ala-D-Glu)-containing adamantyl-triazole moiety and its mannosylated derivative in order to study their immunomodulatory activities in vivo. The adjuvant activity of the prepared compounds was evaluated in a murine model using ovalbumin as an antigen, and compared to the reference adjuvant ManAdDMP. The results showed that the introduction of the lipophilic adamantyl-triazole moiety at the C-terminus of L-Ala-D-Glu contributes to the immunostimulant activity of DMP, and that mannosylation of DMP modified with adamantyl-triazole causes the amplification of its immunostimulant activity.

PMID:34770761 | PMC:PMC8587862 | DOI:10.3390/molecules26216352

Biochem Biophys Res Commun. 2021 Oct 25;583:178-183. doi: 10.1016/j.bbrc.2021.10.050. Online ahead of print.

ABSTRACT

Constant remodeling is necessary for bacterial cell growth and bacterial morphogenesis; peptidoglycan (PG) is a crucial component in this process. Murein DD-endopeptidase (MepS), initially annotated as Spr from E. coli K12, is a NlpC/P60 family endopeptidase, which cleaves the meso-diaminopimelate (DAP)-D-Ala peptide bond of PG. The Cys68, His119, His131 triad form the active site residues. MepS has autolytic activity, which is strictly regulated by a periplasmic degradation system comprising the NlpI/Prc protease complex. MepS is essential for maintaining the cell viability, and therefore, it is a potential target for developing antibiotics. This study aimed to understand the structural basis of substrate recognition and degradation. We determined the high-resolution structures of MepS, after mutating Cys68 to serine (MepS-C68S) to improve stability. We further found that citrate and L-malate molecules bind to the active site of MepS-C68S; this is in line with the recurrent observation of organic acids binding to PG endopeptidases. The presence of conserved residues on the surface revealed the potential peptide binding sites of MepS. We modelled a cross-linked peptide model of meso-DAP-D-Ala-meso-DAP, bound to the active site groove of MepS-C68S. Two conserved tyrosine residues, Tyr56 and Tyr147 appeared to be essential for the recognition of peptides. Our structural discoveries could provide insights for the design of novel antibiotics targeting MepS.

PMID:34741988 | DOI:10.1016/j.bbrc.2021.10.050

Appl Environ Microbiol. 2021 Oct 20:AEM0151521. doi: 10.1128/AEM.01515-21. Online ahead of print.

ABSTRACT

Bacteriophage-encoded lysins are increasingly reported as alternatives to combat Acinetobacter baumannii infections for which limited therapeutic options are available. Some lysins such as LysMK34 have a C-terminal amphipathic helix allowing them to penetrate the otherwise impermeable outer membrane barrier. Another approach to kill Gram-negative pathogens with lysins relies on fusion of a peptide with outer membrane permeabilizing properties to the lysin. In this work, we aimed to leverage the intrinsic antibacterial activity of LysMK34 by fusing the peptide cecropin A to its N-terminus via a linker of three Ala-Gly repeats, resulting in eLysMK34. The engineered lysin has an improved antibacterial activity compared to the parental lysin LysMK34 in terms of minimum inhibitory concentration (0.45 - 1.2 μM), killing rate and killing extent. eLysMK34 has an at least two-fold increased activity against stationary-phase cells and the bactericidal effect becomes less dependent on the intracellular osmotic pressure. Particularly colistin-resistant strains become highly susceptible to eLysMK34 and enhanced antibacterial activity is observed in complement-deactivated human serum. These observations demonstrate that fusion of a lysin with intrinsic antibacterial activity with a selected outer membrane permeabilizing peptide is a useful strategy to further improve the in vitro antibacterial properties of such lysins. Importance Phage lysins are a new class of enzyme-based antibiotics that increasingly gain interest. Lysins kill cells through rapid degradation of the peptidoglycan layer, resulting in sudden osmotic lysis. Whereas Gram-positive bacteria are readily susceptible to the action of lysins, Gram-negative bacteria are naturally resistant as the outer membrane protects their peptidoglycan layer. This work reveals that fusing an outer membrane permeabilizing peptide to a lysin with intrinsic antibacterial activity results in a superior lysin that shows improved robustness in its antibacterial activity, including against the most worrisome colistin-resistant strains A. baumannii.

PMID:34669452 | DOI:10.1128/AEM.01515-21

Comput Struct Biotechnol J. 2021 Sep 17;19:5392-5405. doi: 10.1016/j.csbj.2021.09.018. eCollection 2021.

ABSTRACT

The penicillin-binding proteins are the enzyme catalysts of the critical transpeptidation crosslinking polymerization reaction of bacterial peptidoglycan synthesis and the molecular targets of the penicillin antibiotics. Here, we report a combined crystallographic, small-angle X-ray scattering (SAXS) in-solution structure, computational and biophysical analysis of PBP1 of Staphylococcus aureus (saPBP1), providing mechanistic clues about its function and regulation during cell division. The structure reveals the pedestal domain, the transpeptidase domain, and most of the linker connecting to the "penicillin-binding protein and serine/threonine kinase associated" (PASTA) domains, but not its two PASTA domains, despite their presence in the construct. To address this absence, the structure of the PASTA domains was determined at 1.5 Å resolution. Extensive molecular-dynamics simulations interpret the PASTA domains of saPBP1 as conformationally mobile and separated from the transpeptidase domain. This conclusion was confirmed by SAXS experiments on the full-length protein in solution. A series of crystallographic complexes with β-lactam antibiotics (as inhibitors) and penta-Gly (as a substrate mimetic) allowed the molecular characterization of both inhibition by antibiotics and binding for the donor and acceptor peptidoglycan strands. Mass-spectrometry experiments with synthetic peptidoglycan fragments revealed binding by PASTA domains in coordination with the remaining domains. The observed mobility of the PASTA domain in saPBP1 could play a crucial role for in vivo interaction with its glycosyltransferase partner in the membrane or with other components of the divisome machinery, as well as for coordination of transpeptidation and polymerization processes in the bacterial divisome.

PMID:34667534 | PMC:PMC8493512 | DOI:10.1016/j.csbj.2021.09.018

Microbiol Spectr. 2021 Oct 20:e0052821. doi: 10.1128/Spectrum.00528-21. Online ahead of print.

ABSTRACT

Staphylococcus aureus is an opportunistic pathogen that causes a wide range of infections. Due to the rapid evolution of antibiotic resistance that leads to treatment failure, it is important to understand the underlying mechanisms. Here, the cell wall structures of several laboratory vancomycin-intermediate S. aureus (VISA) strains were analyzed. Among the VISA strains were S. aureus VC40, which accumulated 79 mutations, including most importantly 2 exchanges in the histidine-kinase VraS, and developed full resistance against vancomycin (MIC, 64 μg/ml); a revertant S. aureus VC40R, which has an additional mutation in vraR (MIC, 4 μg/ml); and S. aureus VraS(VC40), in which the 2 vraS mutations were reconstituted into a susceptible background (MIC, 4 μg/ml). A ultraperformance liquid chromatography (UPLC) analysis showed that S. aureus VC40 had a significantly decreased cross-linking of the peptidoglycan. Both S. aureus VC40 and S. aureus VraS(VC40) displayed reduced autolysis and an altered autolysin profile in a zymogram. Most striking was the significant increase in d-alanine and N-acetyl-d-glucosamine (GlcNAc) substitution of the wall teichoic acids (WTAs) in S. aureus VC40. Nuclear magnetic resonance (NMR) analysis revealed that this strain had mostly β-glycosylated WTAs in contrast to the other strains, which showed only the α-glycosylation peak. Salt stress induced the incorporation of β-GlcNAc anomers and drastically increased the vancomycin MIC for S. aureus VC40R. In addition, β-glycosylated WTAs decreased the binding affinity of AtlA, the major autolysin of S. aureus, to the cell wall, compared with α-glycosylated WTAs. In conclusion, there is a novel connection between wall teichoic acids, autolysis, and vancomycin susceptibility in S. aureus. IMPORTANCE Infections with methicillin-resistant Staphylococcus aureus are commonly treated with vancomycin. This antibiotic inhibits cell wall biosynthesis by binding to the cell wall building block lipid II. We set out to characterize the mechanisms leading to decreased vancomycin susceptibility in a laboratory-generated strain, S. aureus VC40. This strain has an altered cell wall architecture with a thick cell wall with low cross-linking, which provides decoy binding sites for vancomycin. The low cross-linking, necessary for this resistance mechanism, decreases the stability of the cell wall against lytic enzymes, which separate the daughter cells. Protection against these enzymes is provided by another cell wall polymer, the teichoic acids, which contain an unusually high substitution with sugars in the β-conformation. By experimentally increasing the proportion of β-N-acetyl-d-glucosamine in a closely related isolate through the induction of salt stress, we could show that the β-conformation of the sugars plays a vital role in the resistance of S. aureus VC40.

PMID:34668723 | DOI:10.1128/Spectrum.00528-21

J Mol Biol. 2021 Oct 21:167319. doi: 10.1016/j.jmb.2021.167319. Online ahead of print.

ABSTRACT

Streptococcus pneumoniae is an opportunistic human pathogen that encodes a single eukaryotic-type Ser/Thr protein kinase StkP and its functional counterpart, the protein phosphatase PhpP. These signaling enzymes play critical roles in coordinating cell division and growth in pneumococci. In this study, we determined the proteome and phosphoproteome profiles of relevant mutants. Comparison of those with the wild-type provided a representative dataset of novel phosphoacceptor sites and StkP-dependent substrates. StkP phosphorylates key proteins involved in cell division and cell wall biosynthesis in both the unencapsulated laboratory strain Rx1 and the encapsulated virulent strain D39. Furthermore, we show that StkP plays an important role in triggering an adaptive response induced by a cell wall-directed antibiotic. Phosphorylation of the sensor histidine kinase WalK and downregulation of proteins of the WalRK core regulon suggest crosstalk between StkP and the WalRK two-component system. Analysis of proteomic profiles led to the identification of gene clusters regulated by catabolite control mechanisms, indicating a tight coupling of carbon metabolism and cell wall homeostasis. The imbalance of steady-state protein phosphorylation in the mutants as well as after antibiotic treatment is accompanied by an accumulation of the global Spx regulator, indicating a Spx-mediated envelope stress response. In summary, StkP relays the perceived signal of cell wall status to key cell division and regulatory proteins, controlling the cell cycle and cell wall homeostasis.

PMID:34688688 | DOI:10.1016/j.jmb.2021.167319

Microb Pathog. 2021 Oct 21;161(Pt A):105260. doi: 10.1016/j.micpath.2021.105260. Online ahead of print.

ABSTRACT

Vibrio parahaemolyticus is responsible for infection diseases of people who consume the contaminated seafood, but its metabolic regulation profile in response to colistin, the last treatment option for multidrug-resistant Gram-negative bacteria, remains unclear. In this study, the metabolic regulation profile of V. parahaemolyticus ATCC33846 under polymyxin B stimulation has been investigated. V. parahaemolyticus exposed to polymyxin B resulted in 4597 differentially transcribed genes, including 673 significantly up-regulated genes and 569 significantly down-regulated genes. In V. parahaemolyticus under polymyxin B stimulation, the cellular antioxidant systems to prevent bacteria from oxidant stress was activated, the synthesis of some nonessential macromolecules was reduced, and the assembly and modification of lipopolysaccharide and peptidoglycan to resist the attack from other antibiotics were promoted. These findings provide new insights into polymyxin B-related stress response in V. parahaemolyticus which should be useful for developing novel drugs for infection.

PMID:34688850 | DOI:10.1016/j.micpath.2021.105260

AIMS Microbiol. 2021 Jul 23;7(3):271-283. doi: 10.3934/microbiol.2021017. eCollection 2021.

ABSTRACT

Lysostaphin is a glycylglycine endopeptidase, secreted by Staphylococcus simulans, capable of specifically hydrolyzing pentaglycine crosslinks present in the peptidoglycan of the Staphylococcus aureus cell wall. In this paper, we describe the cloning and expression of the lysostaphin enzyme gene in Bacillus subtilis WB600 host using pWB980 expression system. Plasmid pACK1 of S. simulans was extracted using the alkaline lysis method. Lysostaphin gene was isolated by PCR and cloned into pTZ57R/T-Vector, then transformed into Escherichia coli DH5α. The amplified gene fragment and uncloned pWB980 vector were digested using PstI and XbaІ enzymes and purified. The restricted gene fragment was ligated into the pWB980 expression vector by the standard protocols, then the recombinant plasmid was transformed into B. subtilis WB600 using electroporation method. The recombinant protein was evaluated by the SDS-PAGE method and confirmed by western immunoblot. Analysis of the target protein showed a band corresponding to 27-kDa r-lysostaphin. Protein content was estimated 91 mg/L by Bradford assay. The recombinant lysostaphin represented 90% of its maximum activity at 40 °C and displayed good thermostability by keeping about 80% of its maximum activity at 45 °C. Heat residual activity assay of recombinant lysostaphin demonstrated that the enzyme stability was up to 40 °C and showed good stability at 40 °C for 16 h incubation.

PMID:34708172 | PMC:PMC8500799 | DOI:10.3934/microbiol.2021017

Proc Natl Acad Sci U S A. 2021 Nov 2;118(44):e2106022118. doi: 10.1073/pnas.2106022118.

ABSTRACT

Bacterial cell wall peptidoglycan is essential, maintaining both cellular integrity and morphology, in the face of internal turgor pressure. Peptidoglycan synthesis is important, as it is targeted by cell wall antibiotics, including methicillin and vancomycin. Here, we have used the major human pathogen Staphylococcus aureus to elucidate both the cell wall dynamic processes essential for growth (life) and the bactericidal effects of cell wall antibiotics (death) based on the principle of coordinated peptidoglycan synthesis and hydrolysis. The death of S. aureus due to depletion of the essential, two-component and positive regulatory system for peptidoglycan hydrolase activity (WalKR) is prevented by addition of otherwise bactericidal cell wall antibiotics, resulting in stasis. In contrast, cell wall antibiotics kill via the activity of peptidoglycan hydrolases in the absence of concomitant synthesis. Both methicillin and vancomycin treatment lead to the appearance of perforating holes throughout the cell wall due to peptidoglycan hydrolases. Methicillin alone also results in plasmolysis and misshapen septa with the involvement of the major peptidoglycan hydrolase Atl, a process that is inhibited by vancomycin. The bactericidal effect of vancomycin involves the peptidoglycan hydrolase SagB. In the presence of cell wall antibiotics, the inhibition of peptidoglycan hydrolase activity using the inhibitor complestatin results in reduced killing, while, conversely, the deregulation of hydrolase activity via loss of wall teichoic acids increases the death rate. For S. aureus, the independent regulation of cell wall synthesis and hydrolysis can lead to cell growth, death, or stasis, with implications for the development of new control regimes for this important pathogen.

PMID:34716264 | DOI:10.1073/pnas.2106022118

Annu Rev Microbiol. 2021 Oct 8;75:151-174. doi: 10.1146/annurev-micro-040621-122027.

ABSTRACT

Most bacteria are protected from environmental offenses by a cell wall consisting of strong yet elastic peptidoglycan. The cell wall is essential for preserving bacterial morphology and viability, and thus the enzymes involved in the production and turnover of peptidoglycan have become preferred targets for many of our most successful antibiotics. In the past decades, Vibrio cholerae, the gram-negative pathogen causing the diarrheal disease cholera, has become a major model for understanding cell wall genetics, biochemistry, and physiology. More than 100 articles have shed light on novel cell wall genetic determinants, regulatory links, and adaptive mechanisms. Here we provide the first comprehensive review of V. cholerae's cell wall biology and genetics. Special emphasis is placed on the similarities and differences with Escherichia coli, the paradigm for understanding cell wall metabolism and chemical structure in gram-negative bacteria.

PMID:34623898 | DOI:10.1146/annurev-micro-040621-122027

Sci Rep. 2021 Jul 5;11(1):13865. doi: 10.1038/s41598-021-93359-6.

ABSTRACT

Staphylococcus aureus is an opportunistic pathogen causing high morbidity and mortality. Since multi-drug resistant S. aureus lineages are nowadays omnipresent, alternative tools for preventive or therapeutic interventions, like immunotherapy, are urgently needed. However, there are currently no vaccines against S. aureus. Surface-exposed and secreted proteins are regarded as potential targets for immunization against S. aureus infections. Yet, many potential staphylococcal antigens of this category do not elicit protective immune responses. To obtain a better understanding of this problem, we compared the binding of serum IgGs from healthy human volunteers, highly S. aureus-colonized patients with the genetic blistering disease epidermolysis bullosa (EB), or immunized mice to the purified S. aureus peptidoglycan hydrolases Sle1, Aly and LytM and their different domains. The results show that the most abundant serum IgGs from humans and immunized mice target the cell wall-binding domain of Sle1, and the catalytic domains of Aly and LytM. Interestingly, in a murine infection model, these particular IgGs were not protective against S. aureus bacteremia. In contrast, relatively less abundant IgGs against the catalytic domain of Sle1 and the N-terminal domains of Aly and LytM were almost exclusively detected in sera from EB patients and healthy volunteers. These latter IgGs may contribute to the protection against staphylococcal infections, as previous studies suggest that serum IgGs protect EB patients against severe S. aureus infection. Together, these observations focus attention on the use of particular protein domains for vaccination to direct potentially protective immune responses towards the most promising epitopes within staphylococcal antigens.

PMID:34226629 | PMC:PMC8257689 | DOI:10.1038/s41598-021-93359-6

ACS Infect Dis. 2021 Jul 7. doi: 10.1021/acsinfecdis.1c00222. Online ahead of print.

ABSTRACT

Bacteriophage endolysins (lysins, or murein hydrolases) are enzymes that bacteriophages utilize to degrade the cell wall peptidoglycans (PG) and subsequently disintegrate bacterial cells from within. Due to their muralytic activity, lysins are considered as potential candidates to battle against antibiotic resistance. However, most lysins in their native form lack the capability of trespassing the outer membrane (OM) of Gram-negative (G-ve) bacteria. To turn the bacteriophage enzymes into antibacterial weapons against G-ve bacteria, endowing these enzymes the capability of accessing the PG substrate underneath the OM is critical. Here we show that fusing a membrane-permeabilizing peptide CeA at the C-terminus of a muralytic enzyme LysAB2 renders a two-step mechanism of bacterial killing and increases the activity of LysAB2 against the multidrug resistant Acinetobacter baumannii by up to 100 000-folds. The engineered LysAB2, termed LysAB2-KWK here, also shows remarkable activity against A. baumannii at the stationary phase and a prominent capability to disrupt biofilm formation. In addition, the enzyme shows a broad antibacterial spectrum against G-ve bacteria, a decent tolerance to serum, and a prolonged storage life. LysAB2-KWK rescues the larva of the greater wax moth Galleria mellonella from A. baumannii infection through systemic administration. Altogether, our work equips a globular lysin with OM permeabilization activity to enable effective killing of G-ve bacteria, reveals the critical role of the C-terminus of a globular lysin in the antibacterial activity, and points toward a viable route to engineer globular lysins as antibacterial enzymes for potential clinical use against multidrug resistant G-ve bacteria.

PMID:34232613 | DOI:10.1021/acsinfecdis.1c00222

ACS Infect Dis. 2021 Jun 30. doi: 10.1021/acsinfecdis.1c00185. Online ahead of print.

ABSTRACT

Commercial carbapenem antibiotics are being used to treat multidrug resistant (MDR) and extensively drug resistant (XDR) tuberculosis. Like other β-lactams, carbapenems are irreversible inhibitors of serine d,d-transpeptidases involved in peptidoglycan biosynthesis. In addition to d,d-transpeptidases, mycobacteria also utilize nonhomologous cysteine l,d-transpeptidases (Ldts) to cross-link the stem peptides of peptidoglycan, and carbapenems form long-lived acyl-enzymes with Ldts. Commercial carbapenems are C2 modifications of a common scaffold. This study describes the synthesis of a series of atypical, C5α modifications of the carbapenem scaffold, microbiological evaluation against Mycobacterium tuberculosis (Mtb) and the nontuberculous mycobacterial species, Mycobacterium abscessus (Mab), as well as acylation of an important mycobacterial target Ldt, Ldt_Mt2. In vitro evaluation of these C5α-modified carbapenems revealed compounds with standalone (i.e., in the absence of a β-lactamase inhibitor) minimum inhibitory concentrations (MICs) superior to meropenem-clavulanate for Mtb, and meropenem-avibactam for Mab. Time-kill kinetics assays showed better killing (2-4 log decrease) of Mtb and Mab with lower concentrations of compound 10a as compared to meropenem. Although susceptibility of clinical isolates to meropenem varied by nearly 100-fold, 10a maintained excellent activity against all Mtb and Mab strains. High resolution mass spectrometry revealed that 10a acylates Ldt_Mt2 at a rate comparable to meropenem, but subsequently undergoes an unprecedented carbapenem fragmentation, leading to an acyl-enzyme with mass of Δm = +86 Da. Rationale for the divergence of the nonhydrolytic fragmentation of the Ldt_Mt2 acyl-enzymes is proposed. The observed activity illustrates the potential of novel atypical carbapenems as prospective candidates for treatment of Mtb and Mab infections.

PMID:34191496 | DOI:10.1021/acsinfecdis.1c00185

Dev Cell. 2021 Jun 28:S1534-5807(21)00485-8. doi: 10.1016/j.devcel.2021.06.007. Online ahead of print.

ABSTRACT

Tissue homeostasis is achieved by balancing stem cell maintenance, cell proliferation and differentiation, as well as the purging of damaged cells. Elimination of unfit cells maintains tissue health; however, the underlying mechanisms driving competitive growth when homeostasis fails, for example, during tumorigenesis, remain largely unresolved. Here, using a Drosophila intestinal model, we find that tumor cells outcompete nearby enterocytes (ECs) by influencing cell adhesion and contractility. This process relies on activating the immune-responsive Relish/NF-κB pathway to induce EC delamination and requires a JNK-dependent transcriptional upregulation of the peptidoglycan recognition protein PGRP-LA. Consequently, in organisms with impaired PGRP-LA function, tumor growth is delayed and lifespan extended. Our study identifies a non-cell-autonomous role for a JNK/PGRP-LA/Relish signaling axis in mediating death of neighboring normal cells to facilitate tumor growth. We propose that intestinal tumors "hijack" innate immune signaling to eliminate enterocytes in order to support their own growth.

PMID:34197724 | DOI:10.1016/j.devcel.2021.06.007

Cell Surf. 2021 Jun 13;7:100055. doi: 10.1016/j.tcsw.2021.100055. eCollection 2021 Dec.

ABSTRACT

The bacterial cell wall contains numerous surface-exposed proteins, which are covalently anchored and assembled by a sortase family of transpeptidase enzymes. The sortase are cysteine transpeptidases that catalyzes the covalent attachment of surface protein to the cell wall peptidoglycan. Among the reported six classes of sortases, each distinct class of sortase plays a unique biological role in anchoring a variety of surface proteins to the peptidoglycan of both pathogenic and non-pathogenic Gram-positive bacteria. Sortases not only exhibit virulence and pathogenesis properties to host cells, but also possess a significant role in gut retention and immunomodulation in probiotic microbes. The two main distinct functions are to attach proteins directly to the cell wall or assemble pili on the microbial surface. This review provides a compendium of the distribution of different classes of sortases present in both pathogenic and non-pathogenic Gram-positive bacteria and also the noteworthy role played by them in bacterial cell wall assembly which enables each microbe to effectively interact with its environment.

PMID:34195501 | PMC:PMC8225981 | DOI:10.1016/j.tcsw.2021.100055

Front Mol Biosci. 2021 Jun 4;8:691569. doi: 10.3389/fmolb.2021.691569. eCollection 2021.

ABSTRACT

Staphylococcus aureus is a leading cause of bacterial infections world-wide. Staphylococcal infections are preferentially treated with β-lactam antibiotics, however, methicillin-resistant S. aureus (MRSA) strains have acquired resistance to this superior class of antibiotics. We have developed a growth-based, high-throughput screening approach that directly identifies cell wall synthesis inhibitors capable of reversing β-lactam resistance in MRSA. The screen is based on the finding that S. aureus mutants lacking the ClpX chaperone grow very poorly at 30°C unless specific steps in teichoic acid synthesis or penicillin binding protein (PBP) activity are inhibited. This property allowed us to exploit the S. aureus clpX mutant as a unique screening tool to rapidly identify biologically active compounds that target cell wall synthesis. We tested a library of ∼50,000 small chemical compounds and searched for compounds that inhibited growth of the wild type while stimulating growth of the clpX mutant. Fifty-eight compounds met these screening criteria, and preliminary tests of 10 compounds identified seven compounds that reverse β-lactam resistance of MRSA as expected for inhibitors of teichoic acid synthesis. The hit compounds are therefore promising candidates for further development as novel combination agents to restore β-lactam efficacy against MRSA.

PMID:34150853 | PMC:PMC8212132 | DOI:10.3389/fmolb.2021.691569

FEBS J. 2021 Jun 10. doi: 10.1111/febs.16066. Online ahead of print.

ABSTRACT

The peptidoglycan (PG) cell wall is an essential polymer for the shape and viability of bacteria. Its protective role is in great part provided by its mesh-like character. Therefore, PG-cross-linking enzymes like the penicillin-binding proteins (PBPs) are among the best targets for antibiotics. However, while PBPs have been in the spotlight for more than 50 years, another class of PG-cross-linking enzymes called LD-transpeptidases (LDTs) seemed to contribute less to PG synthesis and thus, has kept an aura of mystery. In the last years, a number of studies have associated LDTs with cell wall adaptation to stress including β-lactam antibiotics, outer membrane stability, toxin delivery, which has shed light onto the biological meaning of these proteins. Furthermore, as some species display a great abundance of LD-cross-links in their cell wall it has been hypothesized that LDTs could also be the main synthetic PG-transpeptidases in some bacteria. In this review, we introduce these enzymes and their role in PG biosynthesis and we highlight the most recent advances in understanding their biological role in diverse species.

PMID:34109739 | DOI:10.1111/febs.16066