Structures and functions of the membrane-damaging pore-forming proteins

A High-Homology Region Provides the Possibility of Detecting β-Barrel Pore-Forming Toxins from Various Bacterial Species

The pathogenicity of many bacteria, including Bacillus cereus and Staphylococcus aureus, depends on pore-forming toxins (PFTs), which cause the lysis of host cells by forming pores in the membranes of eukaryotic cells. Bioinformatic analysis revealed a region homologous to the Lys171-Gly250 sequence in hemolysin II (HlyII) from B. cereus in over 600 PFTs, which we designated as a "homologous peptide". Three β-barrel PFTs were used for a detailed comparative analysis. Two of them-HlyII and cytotoxin K2 (CytK2)-are synthesized in Bacillus cereus sensu lato; the third, S. aureus α-toxin (Hla), is the most investigated representative of the family. Protein modeling showed certain amino acids of the homologous peptide to be located on the surface of the monomeric forms of these β-barrel PFTs. We obtained monoclonal antibodies against both a cloned homologous peptide and a 14-membered synthetic peptide, DSFNTFYGNQLFMK, as part of the homologous peptide. The HlyII, CytK2, and Hla regions recognized by the obtained antibodies, as well as an antibody capable of suppressing the hemolytic activity of CytK2, were identified in the course of this work. Antibodies capable of recognizing PFTs of various origins can be useful tools for both identification and suppression of the cytolytic activity of PFTs.

Enhanced sensitivity in Staphylococcus aureus detection: Unveiling the impact of lipid composition on the performance of carboxyfluorescein (CF)-Loaded liposome-based assay

Liposomes have emerged as versatile nanocarriers, finding applications not only in drug delivery but also in pathogen detection and diagnostics. This study aimed to enhance the sensitivity of liposomes to Staphylococcus aureus by investigating the impact of lipid composition on liposomes loaded with 5(6)-carboxyfluorescein (CF). Liposomes were fabricated using various concentrations of cholesterol (10-40 mol%) combined with saturated phospholipids. Dynamic light scattering results revealed that higher cholesterol concentrations led to reduced liposome size, CF release (%), and entrapment efficiency (%). Liposome sensitivity towards S. aureus was evaluated by using CF-loaded liposomes with and without aptamer insertion. Liposomes with a higher cholesterol content (40 mol%) exhibited a strong ability to detect low bacterial concentrations down to 5 × 102 CFU/mL without relying solely on specific receptor-ligand recognition. However, functionalizing the liposome with an aptamer further improved the specificity and sensitivity of S. aureus detection at even lower concentrations, down to 80 CFU/mL, in the wide range of 80-107 CFU/mL. This study highlights the potential for optimizing the lipid composition of liposomes to improve their sensitivity for pathogen detection, particularly when combined with aptamer-based strategies.

Genome-Wide Analysis of the Membrane Attack Complex and Perforin Genes and Their Expression Pattern under Stress in the Solanaceae

The Membrane Attack Complex and Perforin (MACPF) proteins play a crucial role in plant development and adaptation to environmental stresses. Heretofore, few MACPF genes have been functionally identified, leaving gaps in our understanding of MACPF genes in other plants, particularly in the Solanaceae family, which includes economically and culturally significant species, such as tomato, potato, and pepper. In this study, we have identified 26 MACPF genes in three Solanaceae species and in the water lily, which serves as the base group for angiosperms. Phylogenetic analysis indicates that angiosperm MACPF genes could be categorized into three distinct groups, with another moss and spikemoss lineage-specific group, which is further supported by the examination of gene structures and domain or motif organizations. Through inter-genome collinearity analysis, it is determined that there are 12 orthologous SolMACPF gene pairs. The expansion of SolMACPF genes is primarily attributed to dispersed duplications, with purifying selection identified as the principal driving force in their evolutionary process, as indicated by the ω values. Furthermore, the analysis of expression patterns revealed that Solanaceae genes are preferentially expressed in reproductive tissues and regulated by various environmental stimuli, particularly induced by submergence. Taken together, these findings offer valuable insights into and a fresh perspective on the evolution and function of SolMACPF genes, thereby establishing a foundation for further investigations into their phenotypic and functional characteristics.

Cryo-EM elucidates mechanism of action of bacterial pore-forming toxins

Pore-forming toxins (PFTs) rupture plasma membranes and kill target cells. PFTs are secreted as soluble monomers that undergo drastic structural rearrangements upon interacting with the target membrane and generate transmembrane oligomeric pores. A detailed understanding of the molecular mechanisms of the pore-formation process remains unclear due to limited structural insights regarding the transmembrane oligomeric pore states of the PFTs. However, recent advances in the field of cryo-electron microscopy (cryo-EM) have led to the high-resolution structure determination of the oligomeric pore forms of diverse PFTs. Here, we discuss the pore-forming mechanisms of various PFTs, specifically the mechanistic details contributed by the cryo-EM-based structural studies.

Membrane Dynamics and Remodelling in Response to the Action of the Membrane-Damaging Pore-Forming Toxins

Pore-forming protein toxins (PFTs) represent a diverse class of membrane-damaging proteins that are produced by a wide variety of organisms. PFT-mediated membrane perforation is largely governed by the chemical composition and the physical properties of the plasma membranes. The interaction between the PFTs with the target membranes is critical for the initiation of the pore-formation process, and can lead to discrete membrane reorganization events that further aids in the process of pore-formation. Punching holes on the plasma membranes by the PFTs interferes with the cellular homeostasis by disrupting the ion-balance inside the cells that in turn can turn on multiple signalling cascades required to restore membrane integrity and cellular homeostasis. In this review, we discuss the physicochemical attributes of the plasma membranes associated with the pore-formation processes by the PFTs, and the subsequent membrane remodelling events that may start off the membrane-repair mechanisms.