The 26S proteasome degrades mouse and yeast ornithine decarboxylase in yeast cells.

Eukaryotic cells possess two high-molecular-mass proteases, the 700 kDa, 20S proteasome, as well as the even larger 1,400 kDa, 26S proteasome. It has been demonstrated that ornithine decarboxylase is degraded, in vitro, by the 26S proteasome that contains the 20S protease as its catalytic core, but not by the free 20S proteasome. Recently, by demonstrating severe inhibition of mouse and yeast ODC degradation in a mutant yeast cell line, defective in the chymotripsin-like activity of the yeast 20S proteasome, we implicated the 20S proteasome in the degradation of ODC, in vivo, in yeast cells.

A unified pathway for the degradation of ornithine decarboxylase in reticulocyte lysate requires interaction with the polyamine-induced protein, ornithine decarboxylase antizyme.

Recent studies have provided convincing evidence to add to a number of earlier observations suggesting that the rapid intracellular degradation of mammalian ornithine decarboxylase (ODC) is further accelerated by the action of ornithine decarboxylase antizyme (ODC-Az), a polyamine-induced protein. However, the mechanism whereby ODC-Az exerts its effect in this proteolytic process is mostly unknown. Here, by using reticulocyte-lysate-based synthesis and degradation systems, we demonstrate that interaction of ODC-Az with ODC results in two related outcomes: (a) ODC is inactivated as a result of its monomerization, and (b) ODC degradation is dramatically accelerated.

The 20S proteasome mediates the degradation of mouse and yeast ornithine decarboxylase in yeast cells.

Ornithine decarboxylase (ODC), a key enzyme in the biosynthesis of polyamines, is one of the most rapidly degraded proteins in mammalian cells. Recently it has been demonstrated that mammalian ODC is degraded in vitro by the 26S protease that contains the 20S proteasome as its catalytic core, in a reaction that does not require ubiquitin. Here, we show that yeast and mouse ODC are both rapidly degraded in yeast cells and that their degradation severely inhibited in a mutant yeast cell line defective in the chymotryptic activity of proteinase yscE, the yeast 20S proteasome.

Gly387 of murine ornithine decarboxylase is essential for the formation of stable homodimers.

In its active form mammalian ornithine decarboxylase (ODC) is a homodimer composed of two 53-kDa subunits while the monomer retains no enzymic activity. In the present study we demonstrate that Gly387 of mouse ODC plays an important role in enabling dimer formation. Gly387 of mouse ODC, an evolutionary conserved residue, was converted to all possible 19 amino acids using site-directed mutagenesis.