Abstract
Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis. Mouse ODC is rapidly degraded in mouse cells, whereas ODC within Trypanosoma brucei, a protozoan parasite infesting cattle, is stable. We have expressed cloned ODC genes of both T. brucei and mouse in ODC-deficient Chinese hamster ovary (CHO) cells. The T. brucei enzyme is stable, whereas the mouse ODC similarly expressed in CHO cells is unstable. This shows that the observed difference in intracellular stability is a property of the ODC protein itself, rather than the cellular environment in which it is expressed. A chimeric ODC composed of the amino terminus of trypanosome and the carboxyl terminus of mouse ODC is rapidly degraded in CHO cells, suggesting that peptide sequences in the mouse ODC carboxyl terminus determine its stability.
Highlights
Trypanosome Ornithine Decarboxylase Is Stable Because It Lacks Sequences Found in the Carboxyl Terminus of the Mouse Enzyme Which Target the Latter For Intracellular Degradation*
FIG. 1. [3,4-3H]DFMO-labeling and 10% SDS-PAGE analysis of trypanosome Ornithine decarboxylase (ODC) protein expressed in Chinese hamster ovary (CHO) cells
The finding that trypanosome ODC expressed in CHO cells is stable in the presence of cycloheximide is similar to the result found for the truncated mouse protein of 424 amino acids
Summary
Trypanosome Ornithine Decarboxylase Is Stable Because It Lacks Sequences Found in the Carboxyl Terminus of the Mouse Enzyme Which Target the Latter For Intracellular Degradation*. The intracellular half-life of mouse ODC is less than 1 h, but it can be extended to over 6 h by a mutation deleting 37 amino acids from the carboxyl terminus [14]. This mutation has the property of rendering that protein more similar to the stable ODC derived from Tryparwsomu brucei, which naturally lacks this 37-amino acid carboxylterminal domain [18, 19]. Mouse and T. brucei ODCs are otherwise remarkably similar in structure: within a common 376-amino acid core region of homology, the enzymes are 69%
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