Upon autophagic stimulation, LC3 becomes conjugated to phosphatidylethanolamine (LC3-II) and localizes at autophagosomal membranes.
On autophagosome formation, LC3-I is cleaved and becomes conjugated to phosphatidylethanolamine to give the form of LC3 termed LC3-II.
Although these data highlight the importance of K127 for ubiquitylation of H2A, they did not establish which of the lysine residues (K125, K127, and K129) becomes conjugated to ubiquitin.
In this pathway, ubiquitin becomes conjugated to target proteins through the sequential action of three types of enzymes – ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin protein ligases (E3) (Glickman and Ciechanover, 2002; Kerscher et al., 2006; Pickart, 2001).
In contrast, the proton in position 3 loses the deshielding effect of a conjugated nitrobenzene group and its singlet peak shifts to higher field (from δ=7.23 ppm to δ=6.75 ppm) as its position becomes conjugated to a second electron-donating bromothiophene group.
After processing, SUMOs become covalently conjugated to cellular targets through a pathway that is similar to ubiquitination.
Mature SUMO proteins become covalently conjugated to other proteins through isopeptide linkage between their C-termini and ε-amino groups of lysines within the targets.
Two distinct mechanisms might target LC3 to the plasma membrane: LC3 may become directly conjugated to the plasma membrane, a scenario that can be demonstrated experimentally but for which no physiological equivalent is known (Fujita et al., 2008), or it may occur by the union of LC3-positive vesicles with the plasma membrane.
Upon induction of autophagy, LC3-I becomes lipid conjugated with phosphatidylethanolamine (PE) into LC3-II, which is then targeted to the membrane of autophagosomes [ 54, 55].
