Renaturation of recombinant secretory leukocyte protease inhibitor: Aspects of disulfide bond formation kinetics

Synthesis of secretory leukocyte protease inhibitor using cell-free protein synthesis system

Secretory leukocyte protease inhibitor (SLPI) functions as a protease inhibitor that modulates excessive proteolysis in the body, exhibits broad-spectrum antimicrobial activity, regulates inflammatory responses, and plays an important role in the innate immunity. The purpose of the study was to artificially synthesize a SLPI, an antimicrobial peptide, and investigate its effect on antimicrobial activity against Porphyromonas gingivalis and interleukin-6 (IL-6) production. SLPI protein with a molecular weight of approximately 13 kDa was artificially synthesized using a cell-free protein synthesis (CFPS) system and investigated by western blotting and enzyme-linked immunosorbent assay (ELISA). Disulfide bond isomerase in the protein synthesis mixture increased the amount of SLPI synthesized. The synthesized SLPI (sSLPI) protein was purified and its antimicrobial activity was investigated based on the growth of Porphyromonas gingivalis and bacterial adhesion to oral epithelial cells. The effect of sSLPI on IL-6 production in human periodontal ligament fibroblasts (HPLFs) was examined by ELISA. Our results showed that sSLPI significantly inhibited the growth of Porphyromonas gingivalis and bacterial adhesion to oral epithelial cells and further inhibited IL-6 production by HPLFs. These results suggested that SLPI artificially synthesized using the CFPS system may play a role in the prevention of periodontal diseases through its antimicrobial and anti-inflammatory effects.

Preparation and characterization of a high-affinity monoclonal antibody against human epididymis protein-4

Human epididymis protein-4 (HE4) may serve as a putative biomarker for the early diagnosis, therapy and especially prognosis of ovarian, lung and breast cancer. Detection and targeting of HE4 using the anti-HE4 antibody could be one of the effective strategies for the cancer diagnosis and treatment in clinical practice. In this study, a high-efficiency expression system was established to purify recombinant HE4. We obtained high purity HE4 in 400 mg quantity from 1 L culture supernatant of HEK293F cells. CCK-8 and cell cycle assays indicated that the purified recombinant HE4 protein could promote SKOV3 cell cycle and proliferation at the concentration of 0.1 mg/L. Furthermore, an anti-HE4 high-affinity monoclonal antibody 9C3 (ka = 8.1 × 10⁶ 1/MS, kd = 4.4 × 10^-5 1/S, KD = 5.5 × 10^-12 M) was prepared using hybridoma technique and analyzed by surface plasmon resonance technology using this HE4 protein. Differential Scanning calorimeter (DSC) analysis showed that 9C3 had a commendable thermal stability with the T_m value of 73 °C. Analyses of western blot, immunohistochemistry and immunofluorescence showed that the 9C3 was highly specific to HE4 in human cancer cells and tissues. In conclusion, our study designed a method to prepare human recombinant HE4 with high yield and generated a high-affinity anti-HE4 monoclonal antibody that might have potential for basic research and clinical application.

Expression and biochemical characterization of recombinant human epididymis protein 4

Whey acidic proteins (WAP) belong to a large gene family of antibacterial peptides that perform critical immune system functions. The function of human epididymis protein 4 (HE4), a 124-amino acid long polypeptide that has two whey acidic protein four-disulfide core (WFDC) domains, is not well studied. Here, a fusion gene encoding the HE4 protein fused to an IgG1 Fc domain was constructed. The recombinant HE4 protein was expressed as a secretory protein in Pichia pastoris and mammalian HEK293-F cells and was subsequently purified. Our data suggested that the HE4 protein produced by these two expression systems bound to both gram-negative and gram-positive bacteria, but demonstrated slightly inhibitory activity towards the growth of Staphylococcus aureus. Moreover, HE4 exhibited proteinase inhibitory activity towards trypsin, elastase, matrix metallopeptidase 9, and the secretory proteinases from Bacillus subtilis. The effects of glycosylation on the biochemical characterization of HE4 were also investigated. LC-ESI-MS glycosylation analysis showed that the high-mannose glycosylated form of HE4 expressed by P. pastoris has lower biological activity when compared to its complex-glycosylated form produced from HEK293-F cells. The implications of this are discussed, which may be provide theoretical basis for its important role in the development of cancer and innate immune system.

Expression and characterization of recombinant human secretory leukocyte protease inhibitor (SLPI) protein from Pichia pastoris

The human secretory leukocyte protease inhibitor (SLPI) has been shown to possess anti-protease, anti-inflammatory and antimicrobial properties. Its presence in saliva is believed to be a major deterrent to oral transmission of human immunodeficiency virus-1. The 11.7kDa peptide is a secreted, nonglycosylated protein rich in disulfide bonds. Currently, recombinant SLPI is only available as an expensive bacterial expression product. We have investigated the utility of the methylotrophic yeast Pichia pastoris to produce and secrete SLPI with C-terminal c-myc and polyhistidine tags. The post-transformational vector amplification protocol was used to isolate strains with increased copy number, and culturing parameters were varied to optimize SLPI expression. Modification of the purification procedure allowed the secreted, recombinant protein to be isolated from the cell-free fermentation medium with cobalt affinity chromatography. This yeast-derived SLPI was shown to have an anti-protease activity comparable to the commercially available bacterial product. Thus, P. pastoris provides an efficient, cost-effective system for producing SLPI for structure function analysis studies as well as a wide array of potential therapeutic applications.

Construction, non-denaturing affinity purification, and characterization of baculovirally expressed human secretory leukocyte protease inhibitor

Secretory leukocyte protease inhibitor (SLPI) is a 11.7 kDa mucosal protein with potent anti-microbial, anti-inflammatory, and wound healing activities. Previous efforts to express and purify the non-glycosylated cationic protein as a recombinant protein in bacteria required extensive denaturation and renaturation to refold the disulfide-rich protein into its biologically active form. To overcome this limitation, we have expressed human SLPI as a polyhistidine-tagged protein (bvHisSLPI) using a recombinant baculovirus expression system. Studies were conducted to determine the timing of maximal protein production following baculovirus infection of Sf21 cells. The 16.4kDa-tagged protein was then overexpressed in Sf21 cells following a 48-h infection with bvHisSLPI-encoding baculovirus, purified by nickel-chelating affinity chromatography under non-denaturing conditions, and analyzed by Coomassie-stained SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot. Purified bvHisSLPI was further characterized by enterokinase digestion to remove the polyhistidine tag from its N-terminus. In serine protease inhibition assays, purified bvHisSLPI blocked substrate cleavage by two serine proteases, chymotrypsin and cathepsin G, comparable to bacterially expressed SLPI. The baculovirus expression and affinity purification strategy described here will facilitate further studies of the structural and biological properties of this important multifunctional protein.