SUMO proteases are a general class of enzymes that specifically remove the post-translational protein modification (PTM) known as small ubiquitin-related modifier (SUMO), which falls into the PTM class of ubiquitin and/or ubiquitin-like proteins (UBL). The enzyme commonly referred to as ‘SUMO protease′ is the Ubl-specific protease 1 (Ulp1) from Saccharomyces cerevisiae. This was the first of this class of enzymes to be isolated. SUMO protease specifically cleaves the SUMO moiety in a ‘scarless′ manner. SUMO protease recognizes the tertiary structure of the Ubiquitin-like SUMO domain and hydrolyzes the peptide bond in the x–Gly–Gly–x sequence after the Gly-Gly bond, at the C-terminus of the SUMO domain. In addition to cleavage of natural SUMO-modified proteins, SUMO protease is used to cleave recombinant SUMO fusion proteins. The SUMO domain is a known solubility-enhancing fusion tag used in recombinant protein expression. A histidine tag can also be added at the N-terminus of the SUMO domain as a purification tag. This SUMO protease product carries a 6x histidine tag. Thus it can be easily removed together with the cleaved SUMO domain, following the digestion reaction
SUMO protease is active over a wide range of temperatures (2–30 °C), ionic strengths (0–400 mM NaCl), and pH ranges (6–8.5). However, its activity may vary depending on the substrate and conditions. Researchers will need to optimize their specific reaction conditions. As an initial suggestion, 20 units of SUMO protease can be used per mg of target protein for 1 hour at 30 °C, or overnight at 2–8 °C. The cleavage efficiency can then be estimated by SDS-PAGE. If necessary, the amount of SUMO protease can then be adjusted. SUMO protease works better in the presence of reducing agents, e.g., 0.5–2 mM DTT. DTT in the reaction mixture can significantly enhance cleavage efficiency, especially during longer incubations
Store the reconstituted product at –20 °C. It is recommended to reconstitute the enzyme in 100 μL of either water or 50% glycerol (v/v), supplemented with 1 mM DTT. Solutions in water/DTT should be stored in frozen aliquots to avoid freeze-thaw cycles, which can adversely affect the protease activity.