Role of Listeriolysin (LLO) in Listeria monocytogenes-infected host cells

• Applicant: Professor Dr. Trinad Chakraborty
• Subject Area: Parasitology and Biology of Tropical Infectious Disease Pathogens
• Term: from 2004 to 2007
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5436155

The major virulence factor of L. monocytogenes listerionlysin (LLO), is a secreted molecule which has functions both extra- and intracellularly. LLO promotes the internalisation of bacteria, escape from the bacteria from the phagososomal vacuole, and escape from the double membrane following spread to neighbouring cells. LLO is the only known member of the cholesterol-dependent cytolysins (CDC) that is produced by an intracellular bacterium. Indeed the activity of LLO cannot be substituted by other CDC toxins such as perfringolysin, and it is likely that the activity of the toxin is modulated during intracellular growth of the bacterium to enable bachterial growth without overt destruction of the eucaryotic cell. The activity of this toxin is mediated by specific subcellular properties: Its activity is high at low pH values (e.g. in the vacuole) and low at neutral pH values (e.g. in the cytoplasm). The PEST-like sequence at the N-terminal end of the molecule has been suggested to modulate the intracytoplsmic activity of LLO by targeting it for degradation. Our studies during the first phase of the Schwerpunkt program revealed yet another property of this sequence, i.e. it is required for efficient transit of LLO from the phagolysosome to the cytoplasm. This was demonstrated by (i) removal of the region harboring the PEST-like sequence which resulted in trapping of the bacterium in the phagolysosome and (ii) addition of the PEST-like sequence region to a related CDC-toxin, pneumolysin, that resulted in an increase in its efficiency to transit to the cytoplasm. Gaining access to the cytoplasm is essential for intracellular growth as protective effects to subsequent challenge with a lethal dose is only observed for bacteria with access to this compartment. Whole genome profiling with purified LLO demonstrated profound effects on cholesterol and lipid metabolism of the eucaryotic cell. We propose that LLO undergoes interactions with host cellular proteins that modulate its intracellular activity. In this proposal we wish to initiate studies that catalog interactions of intracellular host cell proteins and LLO to further understand the molecular mechanisms involved in this modulation.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1131: Life Inside Cells