Abstract

The SUMO proteins are Small Ubiquitin-related MOdifiers that are covalently conjugated onto lysine residues within target sequences. Invertebrates have a single SUMO gene, whereas the SUMO family in vertebrates have three members; SUMO-1, SUMO-2, and SUMO-3. The SUMO proteins are synthesised as inactive precursors, which are processed by SUMO specific carboxy-terminal hydrolases, resulting in novel double-glycine C-termini. The mature SUMO proteins are then activated by an activating enzyme (E1), and transferred to a conjugating enzyme (E2). Eventually, the SUMO protein is covalently linked to the target protein by the formation of an isopeptide bond between the carboxyl terminus of SUMO and an epsilon-amino group of a lysine residue of the target protein. (An E3-like factor that promotes SUMO conjugation has recently been identified (PMID: 11572779).) This process, termed sumoylation, is reversible.

Most sumoylated proteins are nuclear, and three main functional roles of SUMO have been proposed. (i) Protein targeting sumoylation has been shown to be important for nuclear import of the RanGAP1 protein, and for recruiting proteins to subnuclear protein complexes (e.g. promyelocytic leukemia protein (PML) to PML nuclear bodies). (ii) Enhancement of protein stability potential competition with (and inhibition of) ubiquitination. (iii) Transcriptional control (e.g. negative regulation of transcription from the androgen receptor).

A core motif (%KxE) has been identified as the sumoylation target for SUMO-1 (PMID: 11553772, PMID: 11121022, PMID: 10212234). SUMO-2/3 contains a %KxE site, in contrast to SUMO-1, and can thus form polymeric chains (shown in vitro, and in vivo for SUMO-2) (PMID: 11451954).

Recent reviews: PMID: 11031248, PMID: 11265250.

 Selected references

 This ELM has been assigned the following Gene Ontology (GO) terms for biological process, cellular component and molecular function.

Biological Process
negative regulation of transcription	GO:0016481
sumoylation	GO:0016927
protein-nucleus import	GO:0006606
SUMO-dependent protein catabolism	GO:0019940
Cellular Component
nucleus	GO:0005634
PML body	GO:0016605
Molecular Function