Molecular approaches to structure-function analysis of interleukin-8

Comparing freeze drying and spray drying of interleukins using model protein CXCL8 and its variants

Spray-dried products, such as synthetic peptides and hormones, have already been approved by the U.S. Food and Drug Agency and the European Medicines Agency, while spray-dried antibodies or interleukins, are not yet available on the market. Concerning the latter group, knowledge on whether and how spray-drying (SD) can be performed without adversely affecting their biological activity is lacking. Accordingly, this study aimed at establishing a SD process (Büchi B-90 spray dryer) using three Interleukin-8 based proteins (7-74 kDa) that were dispersed in phosphate buffered saline to maintain their stability. A Box-Behnken Design of Experiments was conducted to identify the appropriate process parameters taking into account the thermal stability of interleukin-8. In parallel, a FD process was developed. Both powders were stored for up to 12 weeks. Powder characterization included residual moisture evaluation and the mean particle size of the SD powder was investigated with Laser Diffraction Analysis. The hydrodynamic volume was measured via size exclusion chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The secondary structure of the model proteins in the solid state was assessed with Fourier-transformation infrared spectroscopy for detecting the protein folding patterns and reconstituted with Circular Dichroism Spectroscopy. Finally, the binding affinity was studied with Surface Plasmon Resonance and Isothermal Fluorescence Titration, the protein stability with Chaotropic Unfolding, and the activity studies were carried out with the chemotaxis assay. The results showed that SD and FD powders with a residual moisture of less than 5 wt% were obtained. The interleukins showed no unfolding upon processing, neither in solid state nor reconstituted. Oligomerization was observed for FD, but not for SD interleukins. However, the unfolding, binding affinity and activity of all interleukins examined did not decrease in neither SD nor FD powders, even after 12 weeks of storage. Thus, it can be concluded that SD of interleukin formulations at outlet temperatures close to ambient temperature is a promising process for transferring them into a stable powder.

Fmoc solid-phase synthesis of peptide thioesters using an intramolecularn,S-acyl shift

[reaction: see text] We describe the Fmoc solid-phase synthesis of peptide thioesters based on the alkylation of the safety-catch sulfonamide linker with a protected 2-mercaptoethanol derivative. The thioester is generated on the solid phase after the peptide chain assembly as a consequence of an intramolecular N,S-acyl shift. Depending on the stability of the spacer separating the sulfonamide linker from the resin toward TFA, treatment of the peptidyl resin with TFA led to a soluble or supported deprotected thioester.

The gammaherpesvirus chemokine binding protein can inhibit the interaction of chemokines with glycosaminoglycans

Chemokines are small glycosaminoglycan (GAG) binding proteins that direct the migration of leukocytes by signaling through G protein coupled receptors (GPCR). Many viruses encode proteins that disrupt chemokine responses. The murine gammaherpesvirus-68 gene M3 encodes a chemokine binding protein (vCKBP-3), which has no sequence similarity to chemokine receptors. Initial characterization of vCKBP-3 showed that it inhibits receptor binding and chemokine-induced calcium influx. The structural requirements for the chemokines CXCL8 and CCL2 to bind to vCKBP-3 have been determined. Both chemokines bind to vCKBP-3 via their N-loop, a site that can participate in GAG binding for some chemokines. We have investigated the effect of vCKBP-3 on the interaction of chemokines with GAGs. We found that vCKBP-3 can prevent a range of chemokines from binding to GAGs. Moreover, we also found that vCKBP-3 can displace chemokines from a heparin-coated surface. Together, these data imply that vCKBP-3 can inhibit chemokine activity at two distinct levels. First, it inhibits chemokines from binding to their GPCR. Second, it inhibits their GAG binding and disrupts pre-formed chemokine gradients. This dual ability of vCKBP-3 makes it a more effective inhibitor of chemokine activity.

The gammaherpesvirus chemokine binding protein binds to the N terminus of CXCL8

Viruses encode proteins that disrupt chemokine responses. The murine gammaherpesvirus 68 gene M3 encodes a chemokine binding protein (vCKBP-3) which has no sequence similarity to chemokine receptors but inhibits chemokine receptor binding and activity. We have used a panel of CXCL8 analogs to identify the structural requirements for CXCL8 to bind to vCKBP-3 in a scintillation proximity assay. Our data suggest that vCKBP-3 acts by mimicking the binding of chemokine receptors to CXCL8.

Ligand binding to transmembrane receptors on intact cells or membrane vesicles measured in a homogeneous 1-microliter assay format

We have developed homogeneous miniaturized assays to measure ligand binding to either intact cells or receptor-containing membrane fragments by analysis of particle brightness. As an example, the affinities and inhibition constants of fluorescently labeled interleukin-8 (IL-8) and a low-molecular-weight antagonist toward the receptors CXCR1 and CXCR2, which belong to the superfamily of G protein-coupled receptors (GPCRs), were determined. Although the results were generally comparable between the two approaches, the cell-based measurements revealed a more complex pattern of both ligand and inhibitor titration curves, pointing to the influence of intracellular regulatory events. Both the vesicle- and cell-based membrane receptor assays were successfully miniaturized to a total volume of 1 microl without compromising their sensitivity, indicating that screening of transmembrane receptors in these formats is feasible. This is the first report of a cellular ligand-binding assay performed in such low volumes. The resulting savings in reagent could potentially enable the use of primary cells for future HTS/ultra-HTS efforts.

Comparison of the structure of vMIP-II with eotaxin-1, RANTES, and MCP-3 suggests a unique mechanism for CCR3 activation

Herpesvirus-8 macrophage inflammatory protein-II (vMIP-II) binds a uniquely wide spectrum of chemokine receptors. We report the X-ray structure of vMIP-II determined to 2.1 A resolution. Like RANTES, vMIP-II crystallizes as a dimer and displays the conventional chemokine tertiary fold. We have compared the surface topology and electrostatic potential of vMIP-II to those of eotaxin-1, RANTES, and MCP-3, three CCR3 physiological agonists with known three-dimensional structures. Surface epitopes identified on RANTES to be involved in binding to CCR3 are mimicked on the eotaxin-1 and MCP-3 surface. However, the surface topology of vMIP-II in these regions is markedly different. The results presented here indicate that the structural basis for interaction with the chemokine receptor CCR3 by vMIP-II is different from that for the physiological agonists eotaxin-1, RANTES, and MCP-3. These differences on vMIP-II may be a consequence of its broad-range receptor recognition capabilities.

Protein synthesis by solid-phase chemical ligation using a safety catch linker

The native chemical ligation reaction has been used extensively for the synthesis of the large polypeptides that correspond to folded proteins and domains. The efficiency of the synthesis of the target protein is highly dependent on the number of peptide segments in the synthesis. Assembly of proteins from multiple components requires repeated purification and lyophilization steps that give rise to considerable handling losses. In principle, performing the ligation reactions on a solid support would eliminate these inefficient steps and increase the yield of the protein assembly. A new strategy is described for the assembly of large polypeptides on a solid support that utilizes a highly stable safety catch acid-labile linker. This amide generating linker is compatible with a wide range of N-terminal protecting groups and ligation chemistries. The utility of the methodology is demonstrated by a three-segment synthesis of vMIP I, a chemokine that contains all 20 natural amino acids and has two disulfide bonds. The crude polypeptide product was recovered quantitatively from the solid support and purified in 20%-recovered yield. This strategy should facilitate the synthesis of large polypeptides and should find useful applications in the assembly of protein libraries.