Prokaryotic ubiquitin-like protein
Prokaryotic ubiquitin-like protein (Pup) - functional analog of ubiquitin found in Prokaryote (Mycobacterium tuberculosis). Serves the same function, although the enzymology of ubiquitylation and pupylation is different. In contrast to the three-step reaction of ubiquitylation, pupylation requires two steps, therefore only two enzymes are involved in pupylation. Similar to ubiquitin, Pup attaches to specific lysine residues of substrate proteins by forming isopeptide bonds to target the proteins for proteasomal degradation. Therefore, like Eukaryotes, bacteria may use a small-protein modifier to control protein stability.
|Pup-like protein family|
Three Prokaryotic ubiquitin-like proteins (blue) attached to proteasomal ATPase Mpa (red)
PupDB is a database of pupylated proteins and pupylation sites 
- Pearce, M. J.; Mintseris, J.; Ferreyra, J.; Gygi, S. P.; Darwin, K. H. (2008). "Ubiquitin-Like Protein Involved in the Proteasome Pathway of Mycobacterium tuberculosis". Science 322 (5904): 1104–1107. doi:10.1126/science.1163885. PMC 2698935. PMID 18832610.
- Tung, Chun-Wei (1 January 2012). "PupDB: a database of pupylated proteins". BMC Bioinformatics 13 (1): 40. doi:10.1186/1471-2105-13-40.