LLO

Listeriolysin O (LLO) is a critical virulence factor produced by the bacterium Listeria monocytogenes, the causative agent of listeriosis. This hemolysin is essential for the bacteria's virulence. Encoded by the hlyA gene, LLO is a single polypeptide chain comprising 529 amino acid residues. Classified as a thiol-activated cholesterol-dependent pore-forming toxin, LLO is activated in reducing environments and deactivated in oxidizing environments. Uniquely, LLO achieves maximum cytolytic activity at a pH of 5.5, distinguishing it from other thiol-activated toxins. This characteristic is crucial for its function within the acidic environment of phagosomes (pH ~ 5.9) in infected cells. Once activated within the phagosome, LLO lyses the vesicle, allowing the bacteria to escape into the host cell's cytosol. The neutral pH of the cytosol limits LLO activity, preventing damage to the host cell membrane and enabling intracellular survival of L. monocytogenes. This intracellular localization shields the bacteria from the host's immune defenses, such as antibodies and the complement system. Additionally, LLO induces early-stage histone modifications in the host cell, specifically dephosphorylation of histone H3 and deacetylation of histone H4. These modifications, independent of LLO's pore-forming activity, suppress the expression of genes involved in the inflammatory response. This suggests a role for LLO in modulating the host's immune response to infection. Notably, LLO possesses a 25-residue signal sequence at its N-terminus, essential for secretion. It also contains a PEST-like sequence in the same region, initially thought to target the toxin for degradation. However, recent findings indicate that this PEST-like sequence might regulate LLO production within the cytosol, challenging the initial assumption of its role in LLO degradation.

LLO is a single, non-glycosylated polypeptide chain composed of 529 amino acids, with a molecular weight of 58kDa. (accession number: AAF64524).

A clear solution that has been sterilized by filtration.

The protein solution consists of 50mM NaH₂PO₄, 1mM EDTA, 2.7mM KCl at a pH of 6.4, with 1mM DTT, 5% (v/v) glycerol, and 0.5M NaCl.

For short-term storage (2-4 weeks), the product should be stored at 4°C. For extended storage, freezing at -20°C is recommended. Repeated freezing and thawing should be avoided.

The purity is determined to be higher than 90.0% based on SDS-PAGE analysis.

Recombinant Listeriolysin O exhibited a hemolytic activity of 1.18 x 10⁵ hemolytic units (HU) per milligram of protein. One HU represents the amount of toxin required to release 50% of hemoglobin from erythrocytes, as determined by a hemolysin assay. The toxin can be reactivated using 2mM DTT.

Listeriolysin-O, LLO, hlyA.

Escherichia Coli.