That mechanism, called programmed cell death (PCD), causes a cell to commit suicide. PCD helps organisms contain infections, nip potential cancers in the bud, and get rid of old or unneeded cells. However, runaway PCD leads to everything from unseemly spots on tomatoes to Parkinson's and Alzheimer's diseases.
BTI Scientist and Cornell University Professor of Plant Pathology Gregory Martin studies the interaction of Pseudomonas syringae bacteria with plants to find what determines whether a host succumbs to disease. Martin and graduate student Robert Abramovitch previously found that AvrPtoB, a protein Pseudomonas injects into plants, disables PCD in a variety of susceptible plants and in yeast (a single-celled ancestor of both plants and animals). Abramovitch and Martin compared AvrPtoB's amino acid sequence to known proteins in other microbes and in higher organisms, but found no matches that might hint at how the protein works at the molecular level.
"We had some biochemical clues to what AvrPtoB was doing, but getting the three-dimensional crystal structure was really key," Martin explained. To find that structure, Martin and Abramovitch worked with collaborators at Rockefeller University. The structure of AvrPtoB revealed that the protein looks very much like a ubiquitin ligase, an enzyme plant and animal cells use to attach the small protein ubiquitin to unneeded or defective proteins. Other enzymes then chew up and "recycle" the ubiquitin-tagged proteins.
To confirm that AvrPtoB was a molecular mimic, Martin and Abramovitch altered parts of the
Source:Boyce Thompson Institute for Plant Research