Written by Charlotte Harrison, science writer
The tumour suppressor protein p53 is a key controller of cell proliferation. Mutations that inactivate p53 are found in many human cancers, and so restoring p53 function is an attractive therapeutic strategy. But targeting p53 is hampered by the fact that its 3-dimensional structure is not very stable, which complicates structural biology and drug design studies.
A new paper published in Structure shows that the p53 protein can be stabilized by fusing it with a soluble spider silk protein. This finding could boost drug discovery efforts for the p53 protein, as well as for other proteins that are structurally unstable.
Getting lost in translation
The researchers first focused on the translation of p53. They used an in-vitro translation and ribosome profiling strategy to show that the p53 sequence is translated with poor efficiency. This most likely occurs due to the high proline content of the p53 sequence — which creates structural disorder — and ribosomal stalling during translation.
They then fused the p53 protein to the N-terminal domain of a highly soluble spider silk protein (NT*). The p53–NT* fusion protein was translated with high efficiency and was fully active when expressed in human cancer cells. The main part of the research focused on the mechanisms by which the spider silk protein facilitates the efficient translation of p53.
A spindle and thread mechanism
The authors used a range of biophysical techniques to understand how the structurally disordered region of p53 was affected by the presence of the NT* domain. These methods included crosslinking, conformation-specific antibody studies, electron microscopy, molecular dynamics simulations and nuclear magnetic resonance studies. Overall, they showed that the NT* domain engages in multiple interactions with p53, and that the N-terminus of p53 wraps around the NT* domain.
By wrapping around the NT* domain, p53 is efficiently translated through a mechanism called co-translational folding, which overcomes stalled translation. Essentially, the NT* domain pulls the nascent p53 polypeptide chain through the ribosome and past stalling sites during translation.
Here, the authors used an analogy of a spindle and yarn: the disordered p53 domains — the yarn — wind around the spider silk NT* protein ‘spindle’, and the spindle moves the nascent p53 protein chain along the ribosome during translation.
Moreover, the fusion of NT* to another structurally disordered cancer target, B-Raf, increased its expression, suggesting this strategy might be widely adapted to a range of disordered proteins, thus boosting structural biology studies and drug discovery efforts.
Image Credit: Canva
