Recombinant Proteins
Product List
LLO
Listeriolysin-O Recombinant
LLO is a single, non-glycosylated polypeptide chain composed of 529 amino acids, with a molecular weight of 58kDa. (accession number: AAF64524).
LLO PEST free
Listeriolysin-O PEST free Recombinant
Introduction
Listeriolysin O (LLO) is a hemolysin produced by the bacterium Listeria monocytogenes, the pathogen responsible for causing listeriosis . It is classified as a cholesterol-dependent cytolysin (CDC), a group of toxins produced by various pathogenic Gram-positive bacteria . LLO is crucial for the virulence of L. monocytogenes, enabling the bacterium to escape from the phagosomal compartment of host cells .
Listeriolysin O is a non-enzymatic, cytolytic, thiol-activated toxin that is activated by reducing agents and inhibited by oxidizing agents . Its cytolytic activity is maximized at a pH of 5.5, making it selectively active within the acidic phagosomes of cells that have phagocytosed L. monocytogenes . LLO is encoded by the gene hly, which is part of a pathogenicity island called LIPI-1 . The expression of LLO is regulated by the protein PrfA, which is thermoregulated and maximally active at 37°C .
Listeriolysin O plays a pivotal role in the pathogenicity of Listeria monocytogenes. It enables the bacterium to escape from the phagosomal compartment into the cytoplasm, where it can grow intracellularly . This escape mechanism allows L. monocytogenes to avoid extracellular immune system factors such as the complement system and antibodies . Additionally, LLO causes dephosphorylation of histone H3 and deacetylation of histone H4 during the early phases of infection, downregulating genes involved in the inflammatory response .
Listeriolysin O operates by forming pores in the phagosomal membrane, allowing L. monocytogenes to escape into the cytoplasm . The efficiency and mode of action of LLO as a membrane-disrupting agent are strongly dependent on membrane cholesterol content and environmental pH . LLO can form arc pores and damage membranes as a lineactant, leading to large-scale membrane defects . This process is crucial for the bacterium’s escape from the phagocytic vacuole and subsequent intracellular proliferation .
The expression of LLO is tightly regulated by multiple mechanisms. The gene hly is part of the LIPI-1 pathogenicity island and is controlled by the pleiotropic regulatory activator PrfA . PrfA is thermoregulated, with its translation maximally occurring at 37°C, which is within the range of normal body temperature . Additionally, RNA-mediated regulatory mechanisms play a role in modulating LLO production in response to environmental factors such as oxygen levels and short-chain fatty acids .
Listeriolysin O has several applications in biomedical research and therapeutic strategies. It is used as a model to study intracellular parasitism and cell-mediated immunity . Additionally, LLO is being explored as a component in recombinant vaccines, such as a recombinant BCG vaccine against Mycobacterium tuberculosis that expresses LLO . The inhibition of LLO activity is also being investigated as a potential therapeutic strategy to prevent Listeria monocytogenes infections .
Listeriolysin O is essential throughout the life cycle of Listeria monocytogenes. It facilitates the bacterium’s escape from the phagosomal compartment, allowing it to proliferate within the host cell cytoplasm . This intracellular lifestyle enables L. monocytogenes to evade the host immune response and spread to other cells and tissues . The ability of LLO to modulate host cell signaling and immune responses further enhances the bacterium’s virulence and adaptability .
