Pore-forming peptides: a new treatment option for cancer

: Cancer, as a remaining challenging medical problem, affects millions of people around the world. Cancer cell resistance is one of the main drawbacks in the complete prosperity of even more sophisticated therapies. Pore-forming peptides (PFPs), a group of natural defense system’s proteins used by nearly whole living organisms as antibacterial and antifungal agents, could also be regarded as novel tumoricidal peptides. PFPs approach entails the use of soluble peptides by assembling on mainly target cell membrane and forming potential death-causing pores. Physical damage induction by natural PFPs or their synthetic derivatives could conquer the resistance mechanisms of tumor cells. Given that peptide drugs involve a significant proportion of the pharmaceutical market primarily because of easy synthesis and safety, evaluation of this nature provided model system as a group of anticancer peptides seems a valuable approach. Here, the mode of action of PFPs and their anticancer mechanism are highlighted which is followed by addressing the anticancer studies using PFPs from various sources along with various applied strategies to obtain selective action of PFPs against cancer cells. Challenges and future perspectives of these promising bioactive molecules in cancer treatment are also provided.

Different roles of conserved tyrosine residues of the acylated domains in folding and activity of RTX toxins

Pore-forming repeats in toxins (RTX) are key virulence factors of many Gram-negative pathogens. We have recently shown that the aromatic side chain of the conserved tyrosine residue 940 within the acylated segment of the RTX adenylate cyclase toxin-hemolysin (CyaA, ACT or AC-Hly) plays a key role in target cell membrane interaction of the toxin. Therefore, we used a truncated CyaA-derived RTX719 construct to analyze the impact of Y940 substitutions on functional folding of the acylated segment of CyaA. Size exclusion chromatography combined with CD spectroscopy revealed that replacement of the aromatic side chain of Y940 by the side chains of alanine or proline residues disrupted the calcium-dependent folding of RTX719 and led to self-aggregation of the otherwise soluble and monomeric protein. Intriguingly, corresponding alanine substitutions of the conserved Y642, Y643 and Y639 residues in the homologous RtxA, HlyA and ApxIA hemolysins from Kingella kingae, Escherichia coli and Actinobacillus pleuropneumoniae, affected the membrane insertion, pore-forming (hemolytic) and cytotoxic capacities of these toxins only marginally. Activities of these toxins were impaired only upon replacement of the conserved tyrosines by proline residues. It appears, hence, that the critical role of the aromatic side chain of the Y940 residue is highly specific for the functional folding of the acylated domain of CyaA and determines its capacity to penetrate target cell membrane.

Bacteriocins of Lactic Acid Bacteria as Potent Antimicrobial Peptides against Food Pathogens

An ever-growing demand for food products with minimal chemical additives has generated a necessity for exploring new alternatives for food preservation. In this context, more recently, bacteriocins, the peptides having antimicrobial property, synthesized ribosomally by numerous bacteria have been attracting a lot of attention. They are known to possess the potential to restrict the growth of microorganisms causing food spoilage without causing any harm to the bacteria themselves owing to the presence of self-defensive proteins. In particular, the bacteriocins of lactic acid bacteria have been considered harmless and safe for consumption and are indicated to evade the development of unwanted bacteria. Use of bacteriocins as biopreservatives has been studied in various food industries, and they have been established to elevate the shelf life of minimally processed food items by exerting killing mechanism. They restrict the growth of undesirable bacteria by breaking the target cell membrane and finally resulting into pore formation. The current article provides an insight on bacteriocins of lactic acid bacteria, their biosynthesis, mechanism of action, and promising applications of these antimicrobial peptides in the food sector.

Pathogenesis of extrapulmonary organ damage in SARS-CоV-2 coronavirus infection (analytical review)

Over the past two decades, coronavirus infection has caused two major pandemics: SARS in 2002 and acute respiratory syndrome (MERS) in the Middle East in 2012. In December 2019, the novel coronavirus (CV) SARS-CoV-2 caused an outbreak of pneumonia in Wuhan, China. Experts from the World Health Organization (WHO) have confirmed the risk of this disease for the public health of the entire planet. SARS-CoV-2 was isolated from epithelial cells of the human respiratory tract. It was found that the genotype KB SARS-CoV-2 is closer to bat-SL-CoVZC45 and bat-SL-CoVZXC21, and the spike glycoprotein (SB) of the virus, which determines the ability to bind to the cellular receptor, is similar to the SARS-CoV coronavirus, which is responsible for the outbreak of severe acute respiratory syndrome (SARS / SARS) in 2002]. Angiotensin-converting enzyme 2 (ACE2) is an endogenous spike protein (spike glycoprotein with the S-domain) SARS-CoV-2, which, as part of the ACE2 + SARS-CoV-2 complex, binds to the ACE2 receptor located on the target cell membrane. The article discusses the mechanisms of infection with SARS-CoV-2, cell-cell interactions, and transmission routes. The issues of the epidemiology of COVID-19 and the prospects for the involvement of organs and systems other than the respiratory one in maintaining the viral load are covered in detail. The problems of the immune defense of the human body during infection with SARS-CoV-2 have been identified. Clinical parallels with progenitor viruses, namely SARS-CoV-1 and MERS-CoV, have been drawn. Highlighted risk factors for SARSCoV-2 infection, which make it possible to predict the nature of the course and probable outcomes of COVID-19.

Structural Basis of the Pore-Forming Toxin/Membrane Interaction

With the rapid growth of antibiotic-resistant bacteria, it is urgent to develop alternative therapeutic strategies. Pore-forming toxins (PFTs) belong to the largest family of virulence factors of many pathogenic bacteria and constitute the most characterized classes of pore-forming proteins (PFPs). Recent studies revealed the structural basis of several PFTs, both as soluble monomers, and transmembrane oligomers. Upon interacting with host cells, the soluble monomer of bacterial PFTs assembles into transmembrane oligomeric complexes that insert into membranes and affect target cell-membrane permeability, leading to diverse cellular responses and outcomes. Herein we have reviewed the structural basis of pore formation and interaction of PFTs with the host cell membrane, which could add valuable contributions in comprehensive understanding of PFTs and searching for novel therapeutic strategies targeting PFTs and interaction with host receptors in the fight of bacterial antibiotic-resistance.

Bacteriocins in the Era of Antibiotic Resistance: Rising to the Challenge

Decades of antibiotic misuse in clinical settings, animal feed, and within the food industry have led to a concerning rise in antibiotic-resistant bacteria. Every year, antimicrobial-resistant infections cause 700,000 deaths, with 10 million casualties expected by 2050, if this trend continues. Hence, innovative solutions are imperative to curb antibiotic resistance. Bacteria produce a potent arsenal of drugs with remarkable diversity that are all distinct from those of current antibiotics. Bacteriocins are potent small antimicrobial peptides synthetized by certain bacteria that may be appointed as alternatives to traditional antibiotics. These molecules are strategically employed by commensals, mostly Firmicutes, to colonize and persist in the human gut. Bacteriocins form channels in the target cell membrane, leading to leakage of low-molecular-weight, causing the disruption of the proton motive force. The objective of this review was to list and discuss the potential of bacteriocins as antimicrobial therapeutics for infections produced mainly by resistant pathogens.

Structural basis for effector transmembrane domain recognition by type VI secretion system chaperones

Type VI secretion systems facilitate the delivery of antibacterial effector proteins between neighbouring Gram-negative bacteria. A subset of these effectors harbor N-terminal transmembrane domains (TMDs) implicated in effector translocation across the target cell membrane. However, the abundance and distribution of these TMD-containing effectors has remained unknown. Here we report the discovery of prePAAR, a conserved motif found in over 6,000 putative TMD-containing effectors. Based on their differing sizes and number of TMDs these effectors fall into two distinct classes that are unified by their requirement for a member of the Eag family of T6SS chaperones for export. Co-crystal structures of class I and class II effector TMD-chaperone complexes from Salmonella Typhimurium and Pseudomonas aeruginosa, respectively, reveals that Eag chaperones mimic transmembrane helical packing to stabilize effector TMDs. In addition to participating in the chaperone-TMD interface, we find that prePAAR functions to facilitate proper folding of the downstream PAAR domain, which is required for effector interaction with the T6SS spike. Taken together, our findings define the mechanism of chaperone-assisted secretion of a widespread family of T6SS membrane protein effectors.

Characteristics of the Protein Complexes and Pores Formed by Bacillus cereus Hemolysin BL

Bacillus cereus Hemolysin BL is a tripartite toxin responsible for a diarrheal type of food poisoning. Open questions remain regarding its mode of action, including the extent to which complex formation prior to cell binding contributes to pore-forming activity, how these complexes are composed, and the properties of the pores formed in the target cell membrane. Distinct complexes of up to 600 kDa were found on native gels, whose structure and size were primarily defined by Hbl B. Hbl L1 and L2 were also identified in these complexes using Western blotting and an LC-MS approach. LC-MS also revealed that many other proteins secreted by B. cereus exist in complexes. Further, a decrease of toxic activity at temperatures ≥60 °C was shown, which was unexpectedly restored at higher temperatures. This could be attributed to a release of Hbl B monomers from tight complexation, resulting in enhanced cell binding. In contrast, Hbl L1 was rather susceptible to heat, while heat treatment of Hbl L2 seemed not to be crucial. Furthermore, Hbl-induced pores had a rather small single-channel conductance of around 200 pS and a probable channel diameter of at least 1 nm on planar lipid bilayers. These were highly instable and had a limited lifetime, and were also slightly cation-selective. Altogether, this study provides astonishing new insights into the complex mechanism of Hbl pore formation, as well as the properties of the pores.

COVID-19: viral characterization, pathophysiology and prevention

Introduction: There are seven known species of human coronavirus capable of causing respiratory diseases. The most recent is SARS-CoV-2, the etiologic agent of COVID-19. Objective: To evaluate the main characteristics of SARS-CoV-2, the pathophysiology of COVID-19 and the main measures for prevention and containment of disease progression. Methods: An integrative review was carried out between 2003 and 2020, based on: PubMed, Medline, SciELO, LILACS and Google Academic, using the descriptors: COVID-19, coronavirus, novel coronavirus, human, SARS virus, outbreak disease, viral pneumonia, all listed in MESH and DECS. Results: Of the 65 selected articles, 28 met the inclusion criteria. Conclusion: SARS-CoV-2 is an RNA virus whose protein S is involved in adsorption to the target cell membrane. It is transmitted through contact with contaminated surfaces, secretions or aerosols. In these, it remains viable for three hours, and up to three days on surfaces. Frequent hand washing, disinfecting surfaces, not sharing personal items, social distance of two meters and wearing facemasks when leaving home are recommended. Non-severe patients should be isolated at home for 14 days. Healthcare professionals should use PPE and be careful with potential sources of contamination, including urine and feces of patients during hygiene.

Structural and Functional Analysis of the D614G SARS-CoV-2 Spike Protein Variant

SUMMARYThe SARS-CoV-2 spike (S) protein variant D614G supplanted the ancestral virus worldwide in a matter of months. Here we show that D614G was more infectious than the ancestral form on human lung cells, colon cells, and cells rendered permissive by ectopic expression of various mammalian ACE2 orthologs. Nonetheless, D614G affinity for ACE2 was reduced due to a faster dissociation rate. Assessment of the S protein trimer by cryo-electron microscopy showed that D614G disrupts a critical interprotomer contact and that this dramatically shifts the S protein trimer conformation toward an ACE2-binding and fusion-competent state. Consistent with the more open conformation, neutralization potency of antibodies targeting the S protein receptor-binding domain was not attenuated. These results indicate that D614G adopts conformations that make virion membrane fusion with the target cell membrane more probable but that D614G retains susceptibility to therapies that disrupt interaction of the SARS-CoV-2 S protein with the ACE2 receptor.