To identify which proteins were likely turned on or off during Salmonella infection, the team grew the bacteria either with rich food that satisfied all their nutritional needs or with nutrient-poor food that mimicked the kind of stressful environment the microbes find themselves in while infecting someone.
Then the researchers took samples of the bacteria and identified the proteins inside. They used a method called top-down proteomics, a technological advancement that allows researchers to look at wide swaths of whole proteins instead of just a few at a time. The team identified 563 unique proteins. This number is comparable to fungus and human studies but almost three times as many as in other bacterial studies using top-down proteomics.
They also determined if the proteins had molecular modifications on them. These can cap an end of a protein or dot the protein's length. Because different modifications can be mixed and matched on one protein, they ended up with a total of 1,665 different forms of the 563 unique proteins.
"This study shows how well top-down proteomics works, especially to get at regulatory information," said co-author Liljana Pasa-Tolic, who led top-down proteomics development with mass spectroscopist Si Wu at EMSL, DOE's Environmental Molecular Sciences Laboratory on the PNNL campus.
Gluts Versus Cysts
Of particular interest to the team were S-thiolation modifications. These modifications cover and protect a protein's sulfur atoms, which tend to snag each other like velcro and cause misshapen proteins. The modifications come in two flavors: a bulky glutathione and a compact cysteine. While glutathione modifications are pretty well studied, only four studies reveal cysteine modifications, and only two of those are in bacteria.
A total of 25 proteins sported glutathiones and another 18 wor
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory