Popp also used sortase A to suture PEG chains to the cytokine GCSF-3. When he tested the PEGylated version in mice, it remained in the bloodstream significantly longer and evoked a more robust and prolonged response than a non-PEGylated version. By using sortase A's inherent precision to attach PEG chains, Popp could replace the less precise chemistry-based technique with a highly effective method that should have broader applications.
Next, Popp addressed IFN-alpha 2's thermal stability. Previously, the Ploegh lab stabilized linear polypeptides like IFN-alpha 2 by molecularly gluing their ends together to form circles. A few such cyclic proteins are found in nature. Once circularized, cyclic proteins are often more stable than their linear precursors. This forced looping can interfere with the function of some cell-signaling proteins, but because IFN-alpha 2's binding site is not near its ends, the function of IFN-alpha 2 is unaffected when its ends are joined to form a circle.
To create a cyclic version of IFN-alpha 2, Popp used sortase A to join the two ends of IFN-alpha 2. When he heated the cyclic form of IFN-alpha 2, it was more resistant to breakdown than its linear counterpart and remained biologically potent even after boiling. Popp then tested the circular, PEGylated version and the linear version in mice. The modified version was metabolized more slowly than the linear version and maintained its thermal stability, demonstrating that this simple technique
|Contact: Nicole Giese|
Whitehead Institute for Biomedical Research