Isolation and characterization of human CapG expressed and post-translationally modified in Pichia pastoris

The potential of cold-shock promoters for the expression of recombinant proteins in microbes and mammalian cells

BACKGROUND

Low-temperature expression of recombinant proteins may be advantageous to support their proper folding and preserve bioactivity. The generation of expression vectors regulated under cold conditions can improve the expression of some target proteins that are difficult to express in different expression systems. The cspA encodes the major cold-shock protein from Escherichia coli (CspA). The promoter of cspA has been widely used to develop cold shock-inducible expression platforms in E. coli. Moreover, it is often necessary to employ expression systems other than bacteria, particularly when recombinant proteins require complex post-translational modifications. Currently, there are no commercial platforms available for expressing target genes by cold shock in eukaryotic cells. Consequently, genetic elements that respond to cold shock offer the possibility of developing novel cold-inducible expression platforms, particularly suitable for yeasts, and mammalian cells.

CONCLUSIONS

This review covers the importance of the cellular response to low temperatures and the prospective use of cold-sensitive promoters to direct the expression of recombinant proteins. This concept may contribute to renewing interest in applying white technologies to produce recombinant proteins that are difficult to express.

Expression and purification of active human kinases using Pichia pastoris as a general-purpose host

BACKGROUND

The heterologous expression of human kinases in good purity and in a monomeric, soluble and active form can be challenging. Most of the reported successful attempts are carried out in insect cells as a host. The use of E. coli for expression is limited to a few kinases and usually is facilitated by large solubility tags that can limit biophysical studies and affect protein-protein interactions. In this report, we evaluate the methylotrophic yeast Pichia pastoris (P. pastoris) as a general-purpose host for expression of human kinases.

METHODS

Six diverse kinases were chosen due to their therapeutic importance in human cancers. Tested proteins include serine/threonine kinases cyclin-dependent kinases 4 and 6 (CDK4 and 6) and aurora kinase A (AurKA), receptor tyrosine kinase erbB-2 (HER2), and dual specificity kinase mitogen-activated protein kinase kinase 3 (MKK3b). Noting that positively charged kinases expressed with higher yield, we sought to improve expression of two challenging targets, CDK6 and HER2, by fusing the highly basic, N-terminal domain of the secreted tyrosine-protein kinase VLK. The standard expression procedure for P. pastoris was adopted, followed by purification using affinity chromatography. Purity and activity of the proteins were confirmed and compared to published values.

RESULTS

Some kinases were purified with good yield and purity and with comparable activity to commercially available versions. Addition of the VLK domain improved expression and decreased aggregation of CDK6 and HER2.

Identification of HeLa cell proteins that interact with Chlamydia trachomatis glycogen synthase using yeast two‑hybrid assays

Chlamydia trachomatis (C. trachomatis) is the leading cause of bacterial sexually transmitted diseases and infectious diseases that cause blindness. The pathophysiology of chlamydial infections is poorly understood, but secreted proteins have emerged as key virulence factors. C. trachomatis glycogen synthase (GlgA) is a chlamydial secretory protein, which localizes in the lumen of chlamydial inclusion bodies and the cytosol of host cells. In order to improve understanding of the roles of GlgA in chlamydial pathogenesis, four proteins that interact with GlgA, Homo sapiens CXXC finger protein 1, prohibitin (PHB), gelsolin-like actin-capping protein and apolipoprotein A-I binding protein were identified using yeast two-hybrid assays. The functions of these proteins are complex, and preliminary results suggested that PHB interacts with GlgA. However, further studies are required to determine the specific interactions of these proteins with GlgA. The findings of the present study may provide a direction and foundation for future studies focusing on the mechanism of GlgA in C. trachomatis infection.

Gelsolin-like actin-capping protein has prognostic value and promotes tumorigenesis and epithelial-mesenchymal transition via the Hippo signaling pathway in human bladder cancer

Background:

Transitional cell carcinoma (TCC) of the bladder, the major histologic subtype of bladder cancer, is increasing in incidence and mortality, which requires the identification of effective biomarkers. Actin-regulating proteins have recently been proposed as important antitumor druggable targets. As a gelsolin-family actin-modulating protein, CAPG (gelsolin-like actin-capping protein) generated great interest due to its crucial effects in various biological and physiological processes; however, the role and mechanism of CAPG in TCCs remain unknown.

Materials and methods:

Bioinformatic analysis and immunohistochemistry of clinical specimens were performed to detect the expression level of CAPG. Both in vitro and in vivo assays were used to determine the oncogenic effect of CAPG in TCCs. Male 4–5-week-old BALB/c nude mice were used for in vivo tumorigenesis assays, while SCID mice were used for in vivo metastatic assays. Affymetrix microarray was used to identify the underlying molecular mechanism. Western blot and immunofluorescence were used to validate the expression and localization of proteins.

Results:

CAPG was frequently upregulated in TCCs and associated with clinical aggressiveness and worse prognosis. Functional assays demonstrated that CAPG could contribute to the tumorigenesis, metastasis and epithelial-mesenchymal transition (EMT) of TCCs both in vitro and in vivo. A novel mechanism that CAPG promoted TCC development via inactivating the Hippo pathway, leading to a nucleus translocation of Yes-associated protein was suggested.

Conclusions:

The current study identified CAPG as a novel and critical oncogene in TCCs, supporting the pursuit of CAPG as a potential target for TCC intervention.

Highly efficient extraction and purification of low-density lipoprotein from hen egg yolk

Low-density lipoprotein (LDL) from hen egg yolk has high nutritional value and plays an important role in the fields of biology, medicine, and materials. To develop fundamental research about LDL, a highly efficient extraction method is necessary. We found that 30% saturated ammonium sulfate can extract more crude LDL than 40% saturation. We selected polyethylene glycol (PEG; nonionic type) to obtain crude LDL. Three factors were employed, namely, degree of polymerization, concentration of PEG, and pH of egg yolk plasma. The optimized condition was 5% PEG 4,000 and plasma pH 6.0, and the best extraction efficiency was 68.1 ± 0.5 g lipid /100 g DM and 69.9 ± 2.0% protein. The crude LDL oil of PEG precipitation was very significantly higher (P < 0.01) than ammonium sulfate precipitation (ASP), while there was no significant difference in protein, which indicates that PEG can extract more crude LDL. When ascorbic acid was added, hydrosulfuryl (SH) groups and lipids oxidation degree of crude LDL extracted by PEG (PEG-LDL) was very significantly lower than ASP (P < 0.01). We also obtained both purified LDL and yolk immunoglobulin (IgY) with an appropriate purification column. This paper proposes a highly efficient method to extract LDL with high activity using PEG and ensures co-purification of LDL and IgY.