Expression of soluble proteins in Escherichia coli by linkage with the acidic propiece of eosinophil major basic protein

Toxicity of eosinophil MBP is repressed by intracellular crystallization and promoted by extracellular aggregation

Eosinophils are white blood cells that function in innate immunity and participate in the pathogenesis of various inflammatory and neoplastic disorders. Their secretory granules contain four cytotoxic proteins, including the eosinophil major basic protein (MBP-1). How MBP-1 toxicity is controlled within the eosinophil itself and activated upon extracellular release is unknown. Here we show how intragranular MBP-1 nanocrystals restrain toxicity, enabling its safe storage, and characterize them with an X-ray-free electron laser. Following eosinophil activation, MBP-1 toxicity is triggered by granule acidification, followed by extracellular aggregation, which mediates the damage to pathogens and host cells. Larger non-toxic amyloid plaques are also present in tissues of eosinophilic patients in a feedback mechanism that likely limits tissue damage under pathological conditions of MBP-1 oversecretion. Our results suggest that MBP-1 aggregation is important for innate immunity and immunopathology mediated by eosinophils and clarify how its polymorphic self-association pathways regulate toxicity intra- and extracellularly.

A His6-SUMO-eXact tag for producing human prepro-urocortin 2 in Escherichia coli for raising monoclonal antibodies

This is a first report of recombinant production of human prepro-Urocortin 2 in Escherichia coli by N-terminal fusion with a triple His₆-SUMO-eXact tag and its subsequent use as an antigen for the production and screening of very high affinity monoclonal antibodies. The rationale for this combinatorial construct is that the His tag allows first step protein purification of insoluble and soluble proteins, the SUMO tag enhances protein expression level and solubility, while the eXact tag facilitates anion-triggered on-column cleavage of the triple tag to recover pure native proteins in a simple two-step protein purification procedure. Compared with an eXact fusion alone, the presence of the SUMO moiety enhanced overall expression levels by 4 to 10 fold but not the solubility of the highly basic prepro-Urocortin 2. Insoluble SUMO-eXact-preproUCN2 was purified in milligram quantities by denaturing IMAC and solubilized in native phosphate buffer by on-column refolding or step-wise dialysis. Only a small fraction of this solubilized protein was able to bind onto the eXact™ affinity column and cleaved by NaF treatment. To test whether binding and cleavage failure was due to improperly refolded SUMO-eXact-preproUCN2 or to the presence of N- and C-terminal sequences flanking the eXact moiety, we created a SUMO-eXact-thioredoxin construct which was overexpressed mainly in the soluble form. This protein bound to and was cleaved efficiently on the eXact™ column to yield native thioredoxin. Solubilized SUMO-eXact-preproUCN2 was used successfully to generate two high affinity mouse monoclonal antibodies (KD~10⁻¹⁰ and 10⁻¹¹ M) specific to the pro-region of Urocortin 2.

The chemokine CCL18 causes maturation of cultured monocytes to macrophages in the M2 spectrum

The observation that human monocytes cultured in the presence of the chemokine CCL18 showed increased survival, led us to profile cytokine expression in CCL18-stimulated versus control cultures. CCL18 caused significantly increased expression of chemokines (CXCL8, CCL2, CCL3 and CCL22), interleukin-10 (IL-10) and platelet-derived growth factor, but no up-regulation of M1 cytokines IL-1β or IL-12. CCL18-stimulated monocytes matured into cells with morphological resemblance to IL-4-stimulated macrophages, and expressed the monocyte marker CD14 as well the M2 macrophage markers CD206 and 15-lipoxygenase, but no mature dendritic cell markers (CD80, CD83 or CD86). Functionally, CCL18-stimulated macrophages showed a high capacity for unspecific phagocytosis and for pinocytosis, which was not associated with an oxidative burst. These findings suggest that CCL18-activated macrophages stand at the cross-roads between inflammation and its resolution. The chemokines that are produced in response to CCL18 are angiogenic and attract various leucocyte populations, which sustain inflammation. However, the capacity of these cells to remove cellular debris without causing oxidative damage and the production of the anti-inflammatory IL-10 will initiate termination of the inflammatory response. In summary, CCL18 induces an M2 spectrum macrophage phenotype in the absence of IL-4.