Although the interaction between interleukin-8 (IL-8) and glycosaminoglycans (GAGs) is crucial for the mediation of inflammatory effects, little is known about the site specificity of this interaction. Therefore, we studied complexes of IL-8 and heparin (HEP) as well as other GAGs in a multidisciplinary approach, involving site-directed mutagenesis, mass spectrometry, fluorescence and solution NMR spectroscopy as well as computer modeling. The interaction between GAG and IL-8 is largely driven by the amine groups of the lysine and the guanidinium groups of arginine side chains. However, due to fast exchange with the solvent, it is typically not possible to detect NMR signals of those groups. Here, we applied reductive (13)C-methylation of the lysine side chains providing sensitive NMR probes for monitoring directly the sites of GAG interaction in (1)H-(13)C correlation experiments. We focused on the lysine side chains K25, K28, K59, K69 and K72 of IL-8 (1-77), which were reported to be involved in the binding to GAGs. The NMR signals of these residues were assigned in (1)H-(13)C HSQC spectra through the help of site-directed mutagenesis. NMR and fluorescence titration experiments in combination with molecular docking and molecular dynamics simulations were applied to investigate the involvement of each lysine in the binding with HEP and various GAG hexasaccharides. We identified K25, K69 and K72 to be the most relevant binding anchors of IL-8(1-77) for the analyzed GAGs.

The interactions between regulatory proteins such as interleukin-8 (IL-8) and glycosaminoglycans are of great interest both for the general understanding of regulatory processes in biology and for the development of implant coatings and innovative materials that suppress undesired immune responses and improve wound healing. In previous work, a number of residues of IL-8 that interact strongly with several glycosaminoglycans (GAGs) have been identified. In particular, the negatively charged Glu75 was reported to be involved in interactions with charged GAGs. To improve understanding of the role of this residue, we generated a selectively (15)N-labeled E75K variant of IL-8(1-77) by expressed protein ligation. NMR and fluorescence spectroscopy in combination with molecular modeling were applied to evaluate the particular role of residue 75 in interactions with GAGs. Remarkably, more residues in the variant responded to GAG binding than in the wild-type. For the first time, we identified amino acids 34 to 36 as additional residues in the loop region of IL-8(1-77) that participate in the interactions with GAGs. These findings indicate that the N terminus of the E75K variant is more important as a second binding site for GAGs than that of the wild-type IL-8(1-77).

Preparation of smart materials by coatings of established surfaces with biomolecules will lead to the next generation of functionalized biomaterials. Rejection of implants is still a major problem in medical applications but masking the implant material with protein coatings is a promising approach. These layers not only disguise the material but also equip it with a certain biological function. The anti-inflammatory chemokine stromal cell-derived factor 1α (SDF-1α) is well suited to take over this function, because it efficiently attracts stem cells and promotes their differentiation and proliferation. At least the initial stem cell homing requires the formation of a concentration gradient. Thus, a reliable and robust release mechanism of SDF-1α from the material is essential. Several proteases, most notably matrix metalloproteinases, are upregulated during inflammation, which, in principle, can be exploited for a tightly controlled release of SDF-1α. Herein, we present the covalent immobilization of M-[S4V]-SDF-1α on novel biodegradable polymer films, which consist of heterobifunctional poly(ethylene glycol) and oligolactide-based functionalized macromers. A peptidic linker with a trimeric matrix metalloproteinase 9 (MMP-9) cleavage site (MCS) was used as connection and the linkage between the three components was achieved by combination of expressed protein ligation and Cu(I) catalyzed azide/alkyne cycloaddition. The MCS was used for MMP-9 mediated release of M-[S4V]-SDF-1α from the biomaterial and the released SDF-1α derivative was biologically active and induced strong cell migration, which demonstrates the great potential of this system.

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The chemokine interleukin-8 (IL-8, CXCL8) plays an important role in inflammatory processes and consecutive wound healing. It recruits primarily neutrophils to infection sites and stimulates their degranulation and phagocytosis in effector cells. IL-8 binds glycosaminoglycans (GAGs), a class of complex linear anionic polysaccharides often organized into diversely sulfated micro-domains, that enriches the protein concentration locally and so facilitate the formation of stable concentration gradients. In this study, we applied experimental and computational techniques to investigate the binding of wild type and truncated IL-8 variants to natural and chemically modified GAGs to gain further insight into the IL-8/GAG interaction. Circular dichroism spectroscopy of IL-8 variants did not reveal major structural changes upon GAG binding. Heparin affinity chromatography clearly demonstrates that gradual truncation of the C-terminal helix leads to decreasing affinities. Similarly, surface plasmon resonance indicates participation of both IL-8 termini in GAG binding, which strength is dependent on GAG sulfation degree. Molecular modeling suggests that C-terminal truncation of IL-8 weakens the interaction with GAGs by an alteration of IL-8 GAG binding site. Our study provides more detailed understanding of the IL-8/GAG interaction and contributes to the data of potential use for the development of biomedical implications in tissue regeneration.