"An essential weapon in the body's fight against infection has come into sharper view. Researchers at Princeton University have discovered the 3D structure of an enzyme that cuts to ribbons the genetic material of viruses and helps defend against bacteria. The Princeton team's work has also led to new insights on the enzyme's function. The enzyme is an important player in the innate immune system, a rapid and broad response to invaders that includes the production of a molecule called interferon. Interferon relays distress signals from infected cells to neighboring healthy cells, thereby activating RNase L to turn on its ability to slice through RNA, a type of genetic material that is similar to DNA. The result is new cells armed for destruction of the foreign RNA. The 3D structure uncovered by Korennykh and his team consists of two nearly identical subunits called protomers. The researchers found that one protomer finds and attaches to the RNA, while the other protomer snips it. The initial protomer latches onto one of the four "letters" that make up the RNA code, in particular, the "U," which stands for a component of RNA called uridine. The other protomer "counts" RNA letters starting from the U, skips exactly one letter, then cuts the RNA. Although the enzyme can slice any RNA, even that of the body's own cells, it only does so when activated by interferon. "We were surprised to find that the two protomers were identical but have different roles, one binding and one slicing," Korennykh said. "Enzymes usually have distinct sites that bind the substrate and catalyze reactions. In the case of RNase L, it appears that the same exact protein surface can do both binding and catalysis. One RNase L subunit randomly adopts a binding role, whereas the other identical subunit has no other choice but to do catalysis."
- Quoted from http://phys.org/news/2014-03-slices-dices-body.html#jCp
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