A new protocol for high-yield purification of recombinant human CXCL8((3-72))K11R/G31P expressed in Escherichia coli

A Simple and Efficient System for Producing Recombinant Human CXCL8 in Escherichia coli

Multifunctional pro-inflammatory cytokine CXCL8 is a small peptide of 8-10 kDa in size and it functions as a monomer or dimer. CXCL8 harbors 2 disulfide bonds for its stability. Although production of the CXCL8 protein in a large quantity in both mammalian and bacterial systems has been reported, the processes are complicated and lengthy. Here, we develop a new bacterial expression system for recombinant CXCL8 and simplify the purification system to yield a high amount of protein quickly. The purified CXCL8 protein from our new system develops a crystal structure that is identical to that produced through the mammalian expression system. Thus, we have established a simple and efficient recombinant CXCL8-producing system, which can be easily operated and is suitable to those requiring a large quantity of CXCL8.

The antagonist of CXCR1 and CXCR2 protects db/db mice from metabolic diseases through modulating inflammation

Interleukin-8 (IL-8, also named CXCL8) binds to its receptors (CXCR1 and CXCR2) with subsequent recruitment of neutrophils and enhancement of their infiltration into inflamed sites, which exaggerates inflammation in many diseases. Recent studies have proposed that metabolic disorders can be attenuated by counteracting certain inflammatory signal pathways. In this study, we examined whether intervention with G31P, an antagonist of CXCL8, could attenuate tissue inflammation and development of metabolic disorders in db/db mice. The db/m and db/db mice were subcutaneously injected with G31P or equivalent normal saline once a day for 6 wk. The physical and metabolic parameters, glucose tolerance, insulin sensitivity, hepatic lipid accumulation, and inflammation markers were measured. G31P improved hepatic insulin sensitivity by modulating expression of genes related to gluconeogenesis and phosphorylated Akt levels. The expressions of several genes encoding proteins involved in de novo lipogenesis were decreased in G31P-treated db/db mice. Meanwhile, immune cell infiltration and cytokine release were attenuated in db/db mice with G31P treatment. G31P also improved the ratio of proinflammatory M1 and anti-inflammatory M2 macrophages. Furthermore, G31P ameliorates metabolic disturbances via inhibition of CXCR1 and CXCR2 pathways in db/db mice. These data suggest that the selective inhibition of CXC chemokines may have therapeutic effects on symptoms associated with obesity and diabetes.

CXCR1/CXCR2 antagonist G31P inhibits nephritis in a mouse model of uric acid nephropathy

The prevalence of gout is relatively high worldwide, and many gout patients suffer from uric acid nephropathy (UAN) concomitantly. ELR-CXC chemokines such as CXCL8 and CXCL1 have a elevated expression in UAN. In this research, a mouse UAN model was established for a 12 week duration, and uric acid-related crystals were observed. CXCL8(3-72)K11R/G31P (G31P) is a mutant protein of CXCL8/interleukin 8 (IL-8), which has been reported to have therapeutic efficacy in both inflammatory diseases and malignancies for it acts as a selective antagonist towards CXCR1/CXCR2. In this study, G31P-treated mice showed declined production of the blood urea nitrogen (BUN) level and urine volume in UAN mice compared with G31P-untreated UAN counterparts. In addition, G31P effectively improved renal fibrosis, and reduced uric acid accumulation and leukocyte infiltration in UAN kidneys. Furthermore, the expressions of CXCL1 and CXCL2 were reduced and the activation of NOD-like receptors protein 3 (NLRP3) was inhibited by G31P treatment. This study has demonstrated that G31P attenuates inflammatory progression in chronic UAN, and plays a renoprotective function.

A novel CXCL8-IP10 hybrid protein is effective in blocking pulmonary pathology in a mouse model of Klebsiella pneumoniae infection

Klebsiella pneumoniae (K. pneumoniae) is a hospital-acquired infectious agent that causes a range of diseases. Herein we have developed a novel CXCL8-IP10 hybrid protein and evaluated its efficacy in an animal model of K. pneumoniae infection. Neutrophil chemotaxis data revealed that CXCL8-IP10 could inhibit human neutrophil chemotactic responses induced by the ELR-CXC chemokine CXCL8. To evaluate the effect of CXCL8-IP10 on K. pneumoniae infection, C57BL/6 mice were challenged with K. pneumoniae followed by treatment with CXCL8-IP10 (500 μg/kg, i.p.), or dexamethasone (0.8 mg/kg, s.c.), or ceftazidime (200 mg/kg, s.c.) individually. CXCL8-IP10, dexamethasone or ceftazidime markedly inhibit Klebsiella-induced pulmonary inflammation as assessed by gross examination and histopathology. Moreover, the chemotactic responses of neutrophils was blocked by CXCL8-IP10 rather than dexamethasone or ceftazidime. Furthermore, the levels of inflammatory factors IL-1β, IFN-γ and TNF-α were decreased after CXCL8-IP10, dexamethasone or ceftazidime treatment. Together, these results suggest that CXCL8-IP10 may provide a novel strategy for treating K. pneumoniae infection.

High Level Expression and Purification of the Clinically Active Antimicrobial Peptide P-113 in Escherichia coli

P-113, which was originally derived from the human saliva protein histatin 5, is a histidine-rich antimicrobial peptide with the sequence AKRHHGYKRKFH. P-113 is currently undergoing phase II clinical trial as a pharmaceutical agent to fight against fungal infections in HIV patients with oral candidiasis. Previously, we developed a new procedure for the high-yield expression and purification of hG31P, an analogue and antagonist of human CXCL8. Moreover, we have successfully removed lipopolysaccharide (LPS, endotoxin) associated with hG31P in the expression with Escherichia coli. In this paper, we have used hG31P as a novel fusion protein for the expression and purification of P-113. The purity of the expressed P-113 is more than 95% and the yield is 4 mg P-113 per liter of E. coli cell culture in Luria-Bertani (LB) medium. The antimicrobial activity of the purified P-113 was tested. Furthermore, we used circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy to study the structural properties of P-113. Our results indicate that using hG31P as a fusion protein to obtain large quantities of P-113 is feasible and is easy to scale up for commercial production. An effective way of producing enough P-113 for future clinical studies is evident in this study.

Effects of K11R and G31P Mutations on the Structure and Biological Activities of CXCL8: Solution Structure of Human CXCL8(3-72)K11R/G31P

The ELR-CXC chemokines are important to neutrophil inflammation in many acute and chronic diseases. Among them, CXCL8 (interleukin-8, IL-8), the expression levels of which are elevated in many inflammatory diseases, binds to both the CXCR1 and CXCR2 receptors with high affinity. Recently, an analogue of human CXCL8, CXCL8_(3–72)K11R/G31P (hG31P) has been developed. It has been demonstrated that hG31P is a high affinity antagonist for both the CXCR1 and CXCR2. Herein, we have determined the solution structure and the CXCR1 N-terminal peptide binding sites of hG31P by NMR spectroscopy. We have found that the displacement within the tertiary structure of the 30 s loop and the N-terminal region and more specifically change of the loop conformation (especially H33), of hG31P may affect its binding to the CXCR1 receptor and thereby inhibit human neutrophil chemotactic responses induced by ELR-CXC chemokines. Our results provide a structural basis for future clinical investigations of this CXCR1/CXCR2 receptor antagonist and for the further development of CXCL8 based antagonists.

CXCL8 Antagonist Improves Diabetic Nephropathy in Male Mice With Diabetes and Attenuates High Glucose-Induced Mesangial Injury

Inflammation is recognized as a crucial contribution to diabetic nephropathy (DN). CXCL8 binds to its CXC chemokine receptors (CXCR1 and CXCR2) for recruiting neutrophil infiltration and initiates tissue inflammation. Therefore, we explored the effect of CXCR1 and CXCR2 inhibition on DN. This was achieved by CXCL8(3-72)K11R/G31P (G31P), an antagonist of CXCL8 that has exhibited therapeutic efficacy in inflammatory diseases and malignancies. In this study, we found that renal leukocyte accumulation and rapid increases of CXCL8 occurred in high-fat diet/streptozocin-induced diabetic mice. G31P effectively reduced urine volume, urine albumin/creatinine ratio, blood urea nitrogen, and creatinine clearance rate in mice with diabetes. In addition, renal histopathologic changes including mesangial expansion, glomerulosclerosis, and extracellular matrix deposition were partially moderated in G31P-treated diabetic mice. Furthermore, G31P attenuated renal inflammation and renal fibrosis of diabetic mice by inhibiting proinflammatory and profibrotic elements. G31P also inhibited high glucose-induced inflammatory and fibrotic factor upregulation in human renal mesangial cells. At the molecular level, G31P inhibited activation of CXCR1/2 downstream signaling JAK2/STAT3 and ERK1/2 pathways in in vitro and in vivo experiments. Our results suggest blockade of CXCR1/2 by G31P could confer renoprotective effects that offer potential therapeutic opportunities in DN.

Optimized Triton X-114 assisted lipopolysaccharide (LPS) removal method reveals the immunomodulatory effect of food proteins

SCOPE

Investigations into the immunological response of proteins is often masked by lipopolysaccharide (LPS) contamination. We report an optimized Triton X-114 (TX-114) based LPS extraction method for β-lactoglobulin (BLG) and soy protein extract suitable for cell-based immunological assays.

METHODS AND RESULTS

Optimization of an existing TX-114 based phase LPS extraction method resulted in >99% reduction of LPS levels. However, remaining TX-114 was found to interfere with LPS and protein concentration assays and decreased viability of THP-1 macrophages and HEK-Blue 293 cells. Upon screening a range of TX-114 extraction procedures, TX-114-binding beads were found to most effectively lower TX-114 levels without affecting protein structural properties. LPS-purified proteins showed reduced capacity to activate TLR4 compared to non-treated proteins. LPS-purified BLG did not induce secretion of pro-inflammatory cytokines from THP-1 macrophages, as non-treated protein did, showing that LPS contamination masks the immunomodulatory effect of BLG. Both HEK293 cells expressing TLR4 and differentiated THP-1 macrophages were shown as a relevant model to screen the protein preparations for biological effects of LPS contamination.

CONCLUSION

The reported TX-114 assisted LPS-removal from protein preparations followed by bead based removal of TX-114 allows evaluation of natively folded protein preparations for their immunological potential in cell-based studies.

A fluorescence polarization assay for the experimental validation of an in silico model of the chemokine CXCL8 binding to receptor-derived peptides

Peptide based inhibitors of protein-protein interactions are of great interest in proteomics, structural biology and medicinal chemistry. Optimized inhibitors can be designed by experimental approaches or by computational prediction. Ideally, computational models are adjusted to the peptide-protein complex of interest according to experimental data obtained in specific binding experiments. The chemokine CXCL8 (interleukin-8) is an interesting target for drug discovery due to its role in inflammatory diseases. Given the available structural data and information on its receptor interactions it constitutes a basis for the rational design of inhibitor peptides. Starting from the reported structure of CXCL8 in complex with a peptide derived from its receptor CXCR1 we developed a computational docking procedure to estimate the changes in binding energy as a function of individual amino acid exchanges. This indicates whether the respective amino acid residue must be preserved or can be substituted to maintain or improve affinity, respectively. To validate and improve the assumptions made in this docking simulation we established a fluorescence polarization assay for receptor-derived peptides binding to CXCL8. A peptide library was tested comprising selected mutants characterized by docking simulations. A number of predictions regarding electrostatic interactions were confirmed by these experiments and it was revealed that the model needed to be corrected for backbone flexibility. Therefore, the assay presented here is a promising tool to systematically improve the computational model by iterative cycles of modeling, experimental validation and refinement of the algorithm, leading to a more reliable model and peptides with improved affinity.

Dynamic conformational switching in the chemokine ligand is essential for G-protein-coupled receptor activation

Chemokines mediate diverse functions from organogenesis to mobilizing leucocytes, and are unusual agonists for class-A GPCRs (G-protein-coupled receptors) because of their large size and multi-domain structure. The current model for receptor activation, which involves interactions between chemokine N-loop and receptor N-terminal residues (Site-I) and between chemokine N-terminal and receptor extracellular loop/transmembrane residues (Site-II), fails to describe differences in ligand/receptor selectivity and the activation of multiple signalling pathways. In the present study, we show in neutrophil-activating chemokine CXCL8 that the highly conserved GP (glycine-proline) motif located distal to both N-terminal and N-loop residues couples Site-I and Site-II interactions. GP mutants showed large differences from native-like to complete loss of function that could not be correlated with the specific mutation, receptor affinity or subtype, or a specific signalling pathway. NMR studies indicated that the GP motif does not influence Site-I interactions, but molecular dynamics simulations suggested that this motif dictates substates of the CXCL8 conformational ensemble. We conclude that the GP motif enables diverse receptor functions by controlling cross-talk between Site-I and Site-II, and further propose that the repertoire of chemokine functions is best described by a conformational ensemble model in which a network of long-range coupled indirect interactions mediate receptor activity.