ABSTRACT
The development of novel methods for highly efficient protein purification remains a research focus in the biotechnology field because conventional purification approaches, including affinity purification, gel filtration, and ion-exchange chromatography, require complex manipulation steps and are costly. Here, we describe a simple and rapid protein purification strategy in which the SUMO tag and Ulp1 protease are surface-displayed separately on Escherichia coli cells. After protein induction, the cells are harvested, resuspended in cleavage buffer, and incubated together for cleavage. In this approach, the surface-displayed Ulp1 cleaves the membrane-anchored SUMO fusion protein, resulting in the release of the target protein from the C-terminal of SUMO into the solution. The bacterial cells harboring SUMO and Ulp1 on their surfaces can be easily removed by centrifugation. To evaluate the purification method, we used red fluorescent protein (mCherry). Purified mCherry protein (7.72 ± 1.05 mg from 1 L of bacterial culture) was obtained after only 30 min of incubation. The protein purity was higher than 80%, and could be further improved (> 90%) by simple ultrafiltration. This study offers a promising and simple strategy for the purification of recombinant protein in its native form that requires only cleavage and centrifugation steps.
ABSTRACT
In order to determine the challenge dose of pigeon paramyxovirus type 1 (PPMV-1) inactivated vaccine (S-1 strain). The virus titer of PPMV-1 E5 allantoic fluid (Chuansha strain) was determined using SPF chicken embryos in this research. After inoculating 30-day-old and 120-day-old pigeons with low-HI antibody against PPMV-1 (HI antibody < or =2) with different doses of PPMV-1 (Chuansha strain), the clinical symptoms and histopathological lesions of the challenged pigeons were examined. The results showed that the minimal lethal dose (MLD) of PPMV-1 (Chuansha strain) was 102.5 ELD50, so we determined that 10(5.5) ELD50, which was 1000 times the MLD, could be taken as the challenge dose in the vaccine efficacy test for PPMV-1 inactivated vaccine (S-1 strain).
