Carlos Karan Gurnani Serrano and Matthias Winkle just published their manuscript on ActS.
The integrity of the cell envelope of E. coli relies on the concerted activity of multi‐protein machineries that synthesize the peptidoglycan (PG) and the outer membrane (OM).
Their previous work showed that the depletion of lipopolysaccharide (LPS) export to the OM induces an essential PG remodeling process involving LD‐transpeptidases (LDTs), the glycosyltransferase function of PBP1B and the carboxypeptidase PBP6a. Consequently, cells with defective OM biogenesis lyse if they lack any of these PG enzymes.
Now this research reports that the morphological defects and lysis associated with a ldtF mutant with impaired LPS transport, are alleviated by the loss of the predicted OM‐anchored lipoprotein ActS (formerly YgeR).
It was shown that ActS is an inactive member of LytM‐type peptidoglycan endopeptidases due to a degenerate catalytic domain. ActS is capable of activating all three main periplasmic peptidoglycan amidases, AmiA, AmiB and AmiC, which were previously reported to be activated only by EnvC and/or NlpD. They also suggest that in vivo ActS preferentially activates AmiC and that its function is linked to cell envelope stress.
Review: Lipoproteins in Gram-negative bacteria: new insights into their biogenesis, subcellular targeting and functional roles
Jessica El Rayes and Raquel Rodríguez Alonso just published their review on bacterial lipoproteins.
DpaA detaches Braun's lipoprotein from peptidoglycan
Matthias Winkle, just published his article oin which it was shown that the detachment of Lpp from peptidoglycan is beneficial for the cell under certain stress conditions and that the deletion of dpaA allows frequent transposon inactivation in the lapB (yciM) gene, whose product down-regulates lipopolysaccharide biosynthesis.
DpaA-like proteins have characteristic sequence motifs and are present in many Gram-negative bacteria of which some have no Lpp, raising the possibility that DpaA has other substrates in these species.
Overall, it was shown that the Lpp-peptidoglycan linkage in E. coli is more dynamic than previously appreciated.
The ESR Raquel Rodríguez-Alonso just published a paper on how lipoprotein-β-barrel complexes are formed.
The crystal structure of the key BAM component BamA in complex with RcsF was reported.
BamA adopts an inward-open conformation, with the lateral gate to the membrane closed. RcsF is lodged deep within the lumen of the BamA barrel, binding regions proposed to undergo outward and lateral opening during OMP insertion.
On the basis of their structural and biochemical data, the authors proposed a push-and-pull model for RcsF export following conformational cycling of BamA, and provided a mechanistic explanation for how RcsF uses its interaction with BamA to detect envelope stress. Moreover, it was also suggested that the flux of incoming OMP substrates is involved in the control of BAM activity.
More info: https://www.nature.com/articles/s41589-020-0575-0
The ESRs Elisabete Moura and Tiago Baeta just published a paper on how Thanatin impairs the Lipopolysaccharide Transport Complex Assembly by Targeting LptC-LptA interaction.
Thanatin is a naturally occurring antimicrobial peptide reported to cause defects in membrane assembly and demonstrated in vitro to bind to the N-terminal β-strand of LptA. Since this region is involved in both LptA dimerization and interaction with LptC, the mechanism of inhibition of thanatin was studied to discriminate whether its antibacterial effect is exerted by the disruption of the interaction of LptA with itself or with LptC.
For this purpose, the Bacterial Adenylate Cyclase Two-Hybrid (BACTH) system was implemented to probe in vivo the Lpt interactome in the periplasm.
It was found that thanatin targets both LptC–LptA and LptA–LptA interactions, with a greater inhibitory effect on the former. The disruption of LptC–LptA interaction was confirmed in vitro using two different biophysical techniques. In cells treated with thanatin, LptA undergoes degradation and LPS decorated with colanic acid accumulates. These data further support inhibition or disruption of Lpt complex assembly as the main killing mechanism of thanatin against Gram-negative bacteria.
All the info: https://www.frontiersin.org/articles/10.3389/fmicb.2020.00909/full
Carina Matias is the first PhD student of the T2T network to become a doctor in Microbiology.
She has been working in UNION Therapeutics in Denmark for three years and finally defended her thesis "Antibiotic Drug Development" at Danish Technical University, Novo Nordisk Foundation Center for Biosustainability.
It makes us very happy to watch you chase your dreams!
Tomorrow starts the 2019 Annual Meeting of the Train2Target network.
Students and researchers have spent the last hours travelling to Grenoble, in the heart of the French Alps, for another gathering and discussion of the latest results that they've got.
This year, we have as invited speakers Hans-Georg Sahl (U. Bonn), Joen Luirink (VU-NL), André Zapun (IBS), and from our ITN Cuong Vuong (AiCuris) and Paola Sperandeo (UNIMI).
We expect the meeting to be a great success!