Orlowski Figure 1.
Orlowski Figure 1. The ubiquitin conjugating pathway. . / Proteins destined for degradation through the ubiquitin-proteasome pathway are first labeled with ubiquitin (Ub) tags by the Ub conjugating machinery detailed in this figure. In the initial step, ubiquitin, a highly conserved 8.5 kDa protein, is activated in an ATP-dependent fashion by an E1 Ub activating enzyme, forming a high energy Ub-E1 bond. The thiolester linkage is preserved during the next step, in which the Ub moiety is transferred to an E2 Ub conjugating enzyme. In association with an E3 ubiquitin ligase, the E2 then generally transfers the Ub moiety to an ε-amino group of a specific lysine residue of the target protein. Several cycles of this reaction occur to generate the poly-ubiquitin chains that mark a protein for proteolysis. This figure has been adapted from ScienceSlides 2005 (VisiScience Inc.; www.visiscience.com) with permission of the publisher.

The ubiquitin conjugating pathway.

Proteins destined for degradation through the ubiquitin-proteasome pathway are first labeled with ubiquitin (Ub) tags by the Ub conjugating machinery detailed in this figure. In the initial step, ubiquitin, a highly conserved 8.5 kDa protein, is activated in an ATP-dependent fashion by an E1 Ub activating enzyme, forming a high energy Ub-E1 bond. The thiolester linkage is preserved during the next step, in which the Ub moiety is transferred to an E2 Ub conjugating enzyme. In association with an E3 ubiquitin ligase, the E2 then generally transfers the Ub moiety to an ε-amino group of a specific lysine residue of the target protein. Several cycles of this reaction occur to generate the poly-ubiquitin chains that mark a protein for proteolysis. This figure has been adapted from ScienceSlides 2005 (VisiScience Inc.; www.visiscience.com) with permission of the publisher.

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