|This image shows UBR-box recognition of an arginine residue at the beginning of a protein (blue) targeted for degradation. The structural integrity of the UBR box depends on zinc (grey) and a histidine residue (red) that is mutated in Johanson-Blizzard syndrome. (Credit: Department of Biochemistry, McGill University.)|
"There are lots of reasons cells recycle proteins -- fasting, which causes loss of muscle, growth and remodeling during development, and normal turnover as old proteins are replaced to make new ones," explained lead researcher, Dr. Kalle Gehring, from McGill's Department of Biochemistry. "One way that cells decide which proteins to degrade is the presence of a signal known as an N-degron at the start of the protein. By X-ray crystallography, we discovered that the N-degron is recognized by the UBR box, a component of the cells' recycling system."
The powerful technique can pinpoint the exact location of atoms and enabled the team to capture an image of the UBR box, providing insight to this incredibly tiny yet essential part of our bodies' chemical mechanics.
Aside from representing a major advance in our understanding of the life cycle of proteins, the research has important repercussions for Johanson-Blizzard syndrome, a rare disease that causes deformations and mental retardation. This syndrome is caused by a mutation in the UBR box that causes it to lose an essential zinc atom. Better understanding of the structure of the UBR box may help researchers develop treatments for this syndrome.
The research was published in Nature Structural & Molecular Biology and received funding from the Canadian Institutes of Health Research.