Researchers at Novagen employed a solubility model developed by D.L. Wilkinson and R.G. Harrison to identify E. coli proteins likely to confer the highest solubility on a fusion partner.1 They then narrowed the range of choices based on size and published data, to end up with three candidate proteins: NusA, bacterioferritin (BFR), and GrpE. Western blot and SDS-PAGE analyses revealed that NusA fusion proteins were more soluble than were fusions with either BFR or GrpE, or with thioredoxin (TRX) and glutathione-S-transferase (GST), two proteins traditionally used to increase solubility of target proteins. A 54-kDa tyrosinase was efficiently expressed as a NusA fusion, suggesting that the Nus·Tag may be a good carrier for large, insoluble proteins.
According to Mark Lepinske, marketing communications manager at Novagen, "The primary feature of the new Novagen Nus·Tag System is the tremendous solubility this new tag tends to confer on a target protein. I don't know of another fusion tag for solubility that performs better in lab tests. The peer-reviewed literature on this technology is very compelling."
Novagen's pET 43.1 series includes three separate vectors (pET 43.1a-c(+)). Each encodes a different reading frame to facilitate insert cloning, a His·Tag® to ease purification, and a protease site to remove the tags if desired. These plasmids may be purchased separately for $131. They may also be obtained as part of the pET NusA Fusion System 43.1, which contains all three vectors, a CD containing sequence information, and host strain glycerol stocks. Researchers can purchase this system with ($373) or without ($310) competent cells.