Phosphoprotein-ubiquitin ligase

The phosphoprotein-ubiquitin ligases hgate ubiquitin exclusively to phosphorylated proteins. In this system, ubiquitination and degradation are controlled by the phosphorylation status of the target proteins, which is in turn dependent on the regulated activity of protein kinases (or protein phosphatases). Phosphorylation of the target proteins often occurs in sequence elements rich in the aminoacids P,E,S, and T (PEST sequences). For target proteins and the subunit structure, see 13.3.1. 

There are four types of Ub-protein ligases namely N-end rule E3, hect-Aomasa E3, anaphase promoting complex and phosphoprotein-ubiquitin ligase complex. The main N-end rule E3, E3a is the best characterized ubiquitin ligases. It is approximately a 200-kDa protein that binds N-end rule (Varshavsky, 1996) protein substrates that have basic, i.e. Lys, Arg, His (Type I) or bulky-hydrophobic, i.e. Trp, Phe, Tyr, Leu (Type II) N-terminal... 

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