The ubiquitin-proteasome system specifically degrades cellular proteins, and is commonly disrupted in human diseases. Ubiquitin is a 76 amino acid protein that covalently attaches to proteins and is thought to target and tether them to the proteasome for degradation. Previous work challenged this idea by showing the p21cip1 protein could still be degraded in the absence of lysines, the ubiquitin attachment site. In contrast, lysineless cyclin E was stable. We hypothesized the absence (p21cip1) or presence (cyclin E) of tertiary structure determines whether ubiqutination is required. This model was tested by expressing mutated versions of  p21 and cyclin E in tissue culture cells to measure their stability. Cell extracts were prepared and protein levels determined by western blotting. Our results show that compromising cyclin E structure now allows it to be degraded in the absence of ubiquitination.

Protein structure influences the pathway to the proteasome

243rd National Meeting (2012)

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