Members of the Staphylococcus aureus phenol-soluble modulin (PSM) peptide family are secreted as functional amyloids that serve diverse roles in pathogenicity and may be present as full-length ...peptides or as naturally occurring truncations. We recently showed that the activity of PSMα3, the most toxic member, stems from the formation of cross-α fibrils, which are at variance with the cross-β fibrils linked with eukaryotic amyloid pathologies. Here, we show that PSMα1 and PSMα4, involved in biofilm structuring, form canonical cross-β amyloid fibrils wherein β-sheets tightly mate through steric zipper interfaces, conferring high stability. Contrastingly, a truncated PSMα3 has antibacterial activity, forms reversible fibrils, and reveals two polymorphic and atypical β-rich fibril architectures. These architectures are radically different from both the cross-α fibrils formed by full-length PSMα3, and from the canonical cross-β fibrils. Our results point to structural plasticity being at the basis of the functional diversity exhibited by S. aureus PSMαs.
Curli amyloid fibrils secreted by Enterobacteriaceae mediate host cell adhesion and contribute to biofilm formation, thereby promoting bacterial resistance to environmental stressors. Here, we ...present crystal structures of amyloid-forming segments from the major curli subunit, CsgA, revealing steric zipper fibrils of tightly mated β-sheets, demonstrating a structural link between curli and human pathological amyloids. D-enantiomeric peptides, originally developed to interfere with Alzheimer's disease-associated amyloid-β, inhibited CsgA fibrillation and reduced biofilm formation in Salmonella typhimurium. Moreover, as previously shown, CsgA fibrils cross-seeded fibrillation of amyloid-β, providing support for the proposed structural resemblance and potential for cross-species amyloid interactions. The presented findings provide structural insights into amyloidogenic regions important for curli formation, suggest a novel strategy for disrupting amyloid-structured biofilms, and hypothesize on the formation of self-propagating prion-like species originating from a microbial source that could influence neurodegenerative diseases.
Biofilms are rigid and largely impenetrable three-dimensional matrices constituting virulence determinants of various pathogenic bacteria. Here, we demonstrate that molecular tweezers, unique ...supramolecular artificial receptors, modulate biofilm formation of Staphylococcus aureus. In particular, the tweezers affect the structural and assembly properties of phenol-soluble modulin α1 (PSMα1), a biofilm-scaffolding functional amyloid peptide secreted by S. aureus. The data reveal that CLR01, a diphosphate tweezer, exhibits significant S. aureus biofilm inhibition and disrupts PSMα1 self-assembly and fibrillation, likely through inclusion of lysine side chains of the peptide. In comparison, different peptide binding occurs in the case of CLR05, a tweezer containing methylenecarboxylate units, which exhibits lower affinity for the lysine residues yet disrupts S. aureus biofilm more strongly than CLR01. Our study points to a possible role for molecular tweezers as potent biofilm inhibitors and antibacterial agents, particularly against untreatable biofilm-forming and PSM-producing bacteria, such as methicillin-resistant S. aureus.
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•Molecular tweezers inhibit S. aureus biofilms while not adversely affecting viability•The tweezers inhibit fibrillation of PSMα1, an amyloid peptide in the biofilm matrix•Structural analysis shows distinct fibril inhibition mechanisms by the tweezers•Tweezers disrupt biofilms and reduce virulence of antibiotic-resistant bacteria
Malishev et al. present innovative “molecular tweezers” capable of inhibiting biofilm formation of S. aureus. Comprehensive structural, biophysical, and theoretical analyses reveal distinct effects of the tweezers upon assembly of the PSMα1 functional amyloid, which is the main scaffolding peptide of the bacterial biofilm.
Loss of function (LoF) of TAR-DNA binding protein 43 (TDP-43) and mis-localization, together with TDP-43-positive and hyperphosphorylated inclusions, are found in post-mortem tissue of amyotrophic ...lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients, including those carrying LoF variants in the progranulin gene (GRN). Modeling TDP-43 pathology has been challenging in vivo and in vitro. We present a three-dimensional induced pluripotent stem cell (iPSC)-derived paradigm—mature brain organoids (mbOrg)—composed of cortical-like-astrocytes (iA) and neurons. When devoid of GRN, mbOrgs spontaneously recapitulate TDP-43 mis-localization, hyperphosphorylation, and LoF phenotypes. Mixing and matching genotypes in mbOrgs showed that GRN−/− iA are drivers for TDP-43 pathology. Finally, we rescued TDP-43 LoF by adding exogenous progranulin, demonstrating a link between TDP-43 LoF and progranulin expression. In conclusion, we present an iPSC-derived platform that shows striking features of human TDP-43 proteinopathy and provides a tool for the mechanistic modeling of TDP-43 pathology and patient-tailored therapeutic screening for FTD and ALS.
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•GRN−/− mbOrgs made of mature astrocytes and neurons show traits of TDP-43 pathology•GRN−/− astrocytes are necessary and sufficient for STMN2 mis-splicing in mbOrg•STMN2 mis-splicing is rescued, adding progranulin to neuron and astrocyte co-cultures
In this article, de Majo et al. present a novel 3D iPSC-derived model to study neurodegenerative disorders such as ALS and FTD. When devoid of GRN expression, these cultures present features of ALS- and FTD-associated pathology hardly ever observed in vitro. These phenotypes are shown to be primarily driven by diseased astrocytes and can be rescued by pro-granulin supplementation.
The phenol-soluble modulin (PSM) peptide family, secreted by Staphylococcus aureus, performs various virulence activities, some mediated by the formation of amyloid fibrils of diverse architectures. ...Specifically, PSMα1 and PSMα4 structure the S. aureus biofilm by assembling into robust cross-β amyloid fibrils. PSMα3, the most cytotoxic member of the family, assembles into cross-α fibrils in which α helices stack into tightly mated sheets, mimicking the cross-β architecture. Here we demonstrate that massive T cell deformation and death are linked with PSMα3 aggregation and co-localization with cell membranes. Our extensive mutagenesis analyses support the role of positive charges, and especially Lys17, in interactions with the membrane and suggest their regulation by inter- and intra-helical electrostatic interactions within the cross-α fibril. We hypothesize that PSMα3 cytotoxicity is governed by the ability to form cross-α fibrils and involves a dynamic process of co-aggregation with the cell membrane, rupturing it.
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•The cytotoxic S. aureus PSMα3 assembles into cross-α fibrils•Cross-α fibril polymorphism and mutation-induced secondary structure switching•Regulation by cross-α fibril inter- and intra-helical electrostatic interactions•Toxicity as a putative dynamic process of PSMα3 co-aggregation with membranes
The PSMα3 peptide secreted by the Staphylococcus aureus bacterium attacks human cells via self-assembly into cross-α fibrils that resemble cross-β amyloids involved in neurodegenerative diseases. PSMα3 putatively co-aggregates with membranes, leading to cell damage. This opens ways to design antivirulence agents, which may elicit less resistance compared with conventional antibiotics.
Bacteria often reside in multicellular communities, called biofilms, held together by an extracellular matrix. In many bacteria, the major proteinaceous component of the biofilm are amyloid fibers. ...Amyloids are highly stable and structured protein aggregates which were known mostly to be associated with neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases. In recent years, microbial amyloids were identified also in other species and shown to play major roles in microbial physiology and virulence. For example, amyloid fibers assemble on the bacterial cell surface as a part of the extracellular matrix and are extremely important to the scaffolding and structural integrity of biofilms, which contribute to microbial resilience and resistance. Furthermore, microbial amyloids play fundamental nonscaffold roles that contribute to the development of biofilms underlying numerous persistent infections. Here, we review several nonscaffold roles of bacterial amyloid proteins, including bridging cells during collective migration, acting as regulators of cell fate, as toxins against other bacteria or against host immune cells, and as modulators of the hosts' immune system. These overall points on the complexity of the amyloid fold in encoding numerous activities, which offer approaches for the development of a novel repertoire of antivirulence therapeutics.
Antimicrobial activity is being increasingly linked to amyloid fibril formation, suggesting physiological roles for some human amyloids, which have historically been viewed as strictly pathological ...agents. This work reports on formation of functional cross-α amyloid fibrils of the amphibian antimicrobial peptide uperin 3.5 at atomic resolution, an architecture initially discovered in the bacterial PSMα3 cytotoxin. The fibrils of uperin 3.5 and PSMα3 comprised antiparallel and parallel helical sheets, respectively, recapitulating properties of β-sheets. Uperin 3.5 demonstrated chameleon properties of a secondary structure switch, forming mostly cross-β fibrils in the absence of lipids. Uperin 3.5 helical fibril formation was largely induced by, and formed on, bacterial cells or membrane mimetics, and led to membrane damage and cell death. These findings suggest a regulation mechanism, which includes storage of inactive peptides as well as environmentally induced activation of uperin 3.5, via chameleon cross-α/β amyloid fibrils.
Curli amyloid fibrils secreted by Enterobacteriaceae mediate host cell adhesion and contribute to biofilm formation, thereby promoting bacterial resistance to environmental stressors. Here, we ...present crystal structures of amyloid-forming segments from the major curli subunit, CsgA, revealing steric zipper fibrils of tightly mated beta-sheets, demonstrating a structural link between curli and human pathological amyloids. D-enantiomeric peptides, originally developed to interfere with Alzheimer's disease-associated amyloid-beta, inhibited CsgA fibrillation and reduced biofilm formation in Salmonella typhimurium. Moreover, as previously shown, CsgA fibrils cross-seeded fibrillation of amyloid-beta, providing support for the proposed structural resemblance and potential for cross-species amyloid interactions. The presented findings provide structural insights into amyloidogenic regions important for curli formation, suggest a novel strategy for disrupting amyloid-structured biofilms, and hypothesize on the formation of self-propagating prion-like species originating from a microbial source that could influence neurodegenerative diseases.
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