Researchers at the Johns Hopkins University School of Medicine have determined how the protein Botch regulates the activity of the development-related protein Notch. The results, which were published online April 24th, 2014 in the journal Cell Reports, could have significant implications for our understanding of mammalian development.
Notch refers to a family of four proteins that are highly conserved among mammalian species. These proteins are integrated into cellular membranes and act as receptors for other signaling molecules. When bound to the proper ligand, an intracellular fragment of Notch is cut off, freeing it to initiate important processes within the cell. Among these processes, the most familiar to college undergraduates is the mechanism by which differential Notch signaling leads to either epidermal or neuronal cell fate.
For Notch to be properly inserted into the membrane, glycine, a small amino acid, must be added to the protein in a specific location. An enzyme called furin recognizes this glycine residue and cuts notch near its addition site. This cleaved form of Notch is the molecule that is inserted into the membrane.
According to the Hopkins research team, Botch replaces the glycine residue with another chemical group, 5-oxy-proline. This change physically blocks furlin from cleaving Notch. Thus, Botch activity prevents the proper membrane insertion of Notch.
While regulatory proteins have widely varying molecular effects, they often act in predictable ways: many regulatory actions can be reduced to the addition or removal of a phosphate group or to the physical binding of the regulatory protein to the target molecule. Botch, as a surprise to the Hopkins research team, is unlike any known regulatory molecule. Regulation through the chemical replacement of a glycine residue with a 5-oxy-proline molecule has not been observed before in the world of biochemistry.
The Hopkins research team, led by Valina Dawson and her husband Ted Dawson, both professors of neurology at the Johns Hopkins University School of Medicine’s Institute for Cell Engineering, unexpectedly found Botch when searching for molecules that could protect the brain from injury. Once the protein was isolated, the team looked for other cellular components that interacted with Botch in vivo.
The identification of Botch’s mechanism of regulation will help researchers find other Botch target proteins and look for other enzymes that exert regulatory influence through the same method. This research may have important medical implications as well: further inquiries into Botch activity could lead to treatments for types of leukemia that have been linked to mutations near the pivotal glycine residue.
This research was funded by a McKnight Endowment Fund for Neuroscience Brain Disorders Award, the National Institute of Neurological Disorders and Stroke, the National Institute on Drug Abuse, and the Maryland Stem Cell Research Fund.
