Bacterial protein mimics of DNA, to break through the defense cells

Salmonella infection, often caused by the use or processing nedovrsenoj meat or eggs, affect about 100 million people each year worldwide. The suffering caused by the infection — cramps in stomach, fever and diarrhea — are the result of an extremely accurate set of molecular interactions between bacteria and the infected human cells. In a new study published in the Journal of Biological Chemistry, the scientists from Imperial College London and the Institute of Francis Crick announced some details of how Salmonella closes immune way after infection.

When a pathogen like Salmonella enterica infects a cell, the cell activates a series of signals, the culmination of which is activation of certain genes that cause an immune response. One group of proteins, including immune genes, known as transcription factors NF-kappaβ. Salmonella, however, produces its own set of proteins that prevent this from happening.

How Salmonella infects the cells?

“These bacterial proteins act like a pair of molecular scissors, cutting the transcription factors NF-kappaβ and sabotaging the immune response of infected cells,” says Teresa Thurston, a scientist from Imperial College.

These proteins saboteurs, together called effector proteins metalloprotease zinc work surprisingly delicately for thieves. In human cells, affecting Salmonella enterica, there are five different proteins NF-kappaβ, but Salmonella effectors cut only three of them, leaving the other two untouched.

“Interaction between host and pathogen is very difficult,” says Thurston. “So, the bacterial proteins able to influence a certain part of the immune response, leaving the others untouched. Accordingly, they are very exactly adjusted to the immune response of the carrier that leads to carpet bombing”.

Scientists have found a clever molecular mechanism of sabotage. Transcription factors NF-kappaB include immune system genes, being bound to DNA in certain places. Salmonella effector proteins adopt a specific shape and electrical charge of the DNA backbone by tricking the proteins NF-kappaB and causing them to cling to itself; once this occurs, a protein of Salmonella cuts the protein NF-kappaB.

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