Ubiquitin-like modifiers and their deconjugating enzymes in medically important parasitic protozoa

Protein modification by ubiquitin and ubiquitin-like proteins is one of the most complex and intensely studied mechanisms of posttranslational protein regulation in eukaryotes. Conjuga-tion of the 76-amino-acid protein ubiquitin is first and fore-most a signal for targeting proteins to the proteasome for degradation, but evidence that ubiquitin also plays diverse roles in the regulation of numerous biological pathways is building. In addition, there are many structurally related ubiq-uitin-like modifiers (Ubls) that utilize mechanistic pathways similar to those utilized by ubiquitin for conjugation to protein substrates and deconjugation. Despite similarities in structure between ubiquitin and other Ubls, modification by Ubls regu-lates such diverse cellular processes as transcriptional regula-tion, cell cycle control, and autophagy (see Kerscher et al. [22] for a review of Ubls and known functions). Ubiquitin has bee