In eukaryotes, endogenous SUMO proteases rapidly cleave SUMO fusions in vivo, precluding tag-enhanced expression and purification capacities. To circumvent this problem, LifeSensors has engineered the SUMOstar fusion system. SUMOstar offers the same solubility and expression enhancing benefits as the original wild-type SUMO tag; however, the tag is not cleaved by endogenous eukaryotic SUMO proteases. In addition, LifeSensors has created a cognate SUMOstar protease for specific recognition and cleavage of the SUMOstar tag in vitro, liberating the protein-of-interest with a desired N-terminal amino acid. The pM-Mammalian Secretory SUMOstar kit allows for expression and secretion of SUMOstar fusion proteins.