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. 2020 Aug 6;10(8):1154. doi: 10.3390/biom10081154

Figure 1.

Figure 1

The Small Ubiquitin-like Modifier (SUMO) conjugation cycle: The names of the enzymes are based on mammalian nomenclature. After SUMO cleavage (not shown), SUMO is conjugated to a heterodimeric E1 ligase complex (SAE1/2). Next, SUMO is transferred to the E2 ligase (Ubc9). Finally, the SUMO-Ubc9 molecule forms a complex with an E3 ligase (e.g., PISA1–4) and with the target protein. This complex formation facilitates the transfer of SUMO to a specific lysine residue on the sequence of the target protein. Alternatively, SUMO conjugation to the E2 ligase, Ubc9, can be followed by the direct transfer of SUMO to the protein target independently of E3 ligase activity. Substrates can be conjugated with a single SUMO (monoSUMOylation), with multiple SUMO peptides on different lysine residues (multiSUMOylation), or with a chain of SUMO2/3 tags (polySUMOylation). SUMO-specific proteases (named SENtrin-specific Proteases (SENPs) in mammals and Ubiquitin-Like Proteases (ULPs) in nonmammalian organisms cleave SUMO from its protein substrate in order to reverse SUMO conjugation and activity.