Comparative study of the insoluble and soluble Ulp1 protease constructs as Carrier free and dependent protein immobilizates.

In this study， we analyzed and compared the properties of yeast Ulp1 protease in active inclusion bodies (IBs) as special protein immobilizate， and the soluble Ulp1 via oriented immobilization. Fusion of the N-terminal self-assembling peptide GFIL8 to the Ulp1 increased production of active IBs in Escherichia coli. Attachment of the N-terminal cellulose-binding module facilitated the constructed protein immobilized on the regenerated amorphous cellulose (RAC) with a binding capacity up to about 235 mg protein per gram of RAC. Compared with the immobilized soluble construct， the insoluble Ulp1 showed higher resistance to limited proteolysis with trypsin digestion， lower leaky amount at different storage temperatures， but more rapid decrease in cleavage activity after stored at 4°C for 8 days. The immobilized soluble Ulp1 maintained about 42% initial cleavage activity with repetitive use successively， whereas the aggregated Ulp1 lost its cleavage capacity after cleaving the protein substrate once. Crosslinking of IBs mediated by glutaraldehyde inactivated the Ulp1. Freshly prepared and used IBs showed similar resistance to protease-K digestion， and comparable binding capacity of Congo red and thioflavin T. Taken together， due to different advantages， the Ulp1 constructs as carrier-free and carrier-dependent immobilizates are used under different conditions.