Small ubiquitin-like modifier SUMO

Small Ubiquitin-like modifier (SUMO) is a conserved protein that is ubiquitously expressed in eukaryotes and is essential for viability. It serves as a reversible posttranslational modifier by forming an isopeptide bond with lysine residues in many target proteins, in a catalytic process termed SUMOylation. SUMOylation of proteins results in altered inter- or intramolecular interactions of the modified target (Fig. 1). 

Histones are also modified by the small ubiquitin-like modifier (SUMO). SUMO-speeifie aetivating, eonjugating and ligating enzymes catalyse the ligation of SUMO proteins to lysines in histones, particularly in histone H4, where SUMOylation is associated with transcriptional repression, through the recruitment of HDACs and HPl. ... 

Sampson, D. A., Wang, M., and Matunis, M. J. (2001). The small ubiquitin-like modifier-1 (SUMO-1) consensus sequence mediates Ubc9 binding and is essential for SUMO-1 modification. / Biol. Chem. 276, 21664-21669. 

SUMOylation is a post-translational modification involved in various cellular processes, such as nuclear-cytosolic transport, transcriptional regulation, apoptosis, protein stability, response to stress and progression through the cell cycle. Small ubiquitin-like modifier or SUMO proteins are a family of small proteins that are covalently attached to and detached from other proteins in cells to modify their function. 

Small tfbiquitin-like modifier represents a family of evolutionary conserved proteins that are distantly related in amino-acid sequence to ubiquitin, but share the same structural folding with ubiquitin proteins. SUMO proteins are covalently conjugated to protein substrates by an isopeptide bond through their carboxyl termini. SUMO addition to lysine residues of target proteins, termed SUMOylation, mediates post-transla-tional modification and requires a set of enzymes that are distinct from those that act on ubiquitin. SUMOylation regulates the activity of a variety of tar get proteins including transcription factors. 

Another protein modification, which occurs through a three-enzyme complex similar to that required for ubiquitin addition, is SUMOylation. SUMO stands for small ubiqutin-like modifier, and when proteins are tagged with SUMO their activites are altered (either positively or negatively, depending on the protein). SUMOylation presents yet another means of fine-tuning existing regulatory systems. 

Common posttranslational modifications of proteins. Frequently modified amino adds for each moiety are described. Most modifications involve low-mass substituents (<500amu), but some modifications are small polypeptides of considerable mass such as ubiquitin or highly related peptide isomers like SUMO-1, SUMO-2, and SUMO 3. SUMO is the abbreviation for similar to ubiquitin methyl organizer , SUMO has different family members (SUMO 1, 2, and 3 that can combine with proteins). 

Sumoylation is a covalent modification of proteins that is related to, but functionally distinct from ubiquitination (review Wilson and Rangasami, 2001). As in ubiquitinylation, sumoylation involves the covalent attachment of a small protein moiety, termed SUMO, to target proteins. The reactions leading to sumoylation of substrate proteins are related to those involved in ubiquitination. El- and E2 like enzymes are responsible for the attachment of the SUMO moiety to lysine residues of the target protein. As compared to ubiquitination, sumolyation is more sequence specific and requires a particular amino acids in the neighbourhood of the lysine to be modified. 

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