Prokaryotic ubiquitin-like protein

Prokaryotic ubiquitin-like protein (Pup) is a functional analog of ubiquitin found in the prokaryote Mycobacterium tuberculosis. Like ubiquitin, Pup serves to direct proteins to the proteasome for degradation in the Pup-proteasome system (PPS). However, the enzymology of ubiquitylation and pupylation is different, owing to their distinct evolutionary origins. In contrast to the three-step reaction of ubiquitylation, pupylation requires only two steps, and thus only two enzymes are involved in pupylation. The enzymes involved in pupylation are descended from glutamine synthetase.

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