Ubiquitin Isopeptide Hydrolysis

The channel through the proteasome a-ring into the central chamber measures 1.3 nm in diameter, a size too small to permit passage of a folded protein, even one as 

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Ubiquitin is highly conserved in eukaryotes yeast and human ubiquitin differ at only 3 of 76 residues. The carboxyl-terminal glycine residue of ubiquitin (Ub) becomes covalently attached to the e-amino groups of several lysine residues on a protein destined to be degraded. The energy for the formation of these isopeptide bonds (iso because e- rather than a-amino groups are targeted) comes from ATP hydrolysis. 

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