Conservation of Functional Sites on Interleukin-6 and Implications for Evolution of Signaling Complex Assembly and Therapeutic Intervention |
| |
Authors: | Vaclav Veverka Terry Baker Nicholas T Redpath Bruce Carrington Frederick W Muskett Richard J Taylor Alastair D G Lawson Alistair J Henry Mark D Carr |
| |
Institution: | From the ‡Department of Biochemistry, University of Leicester, Henry Wellcome Building, Lancaster Road, Leicester LE1 9HN, United Kingdom.;¶UCB Pharma, 213 Bath Road, Slough SL1 4EN, United Kingdom, and ;the §Institute of Organic Chemistry and Biochemistry, Flemingovo namesti 2, 166 10 Prague 6, Czech Republic |
| |
Abstract: | A number of secreted cytokines, such as interleukin-6 (IL-6), are attractive targets for the treatment of inflammatory diseases. We have determined the solution structure of mouse IL-6 to assess the functional significance of apparent differences in the receptor interaction sites (IL-6Rα and gp130) suggested by the fairly low degree of sequence similarity with human IL-6. Structure-based sequence alignment of mouse IL-6 and human IL-6 revealed surprising differences in the conservation of the two distinct gp130 binding sites (IIa and IIIa), which suggests a primacy for site III-mediated interactions in driving initial assembly of the IL-6/IL-6Rα/gp130 ternary complex. This is further supported by a series of direct binding experiments, which clearly demonstrate a high affinity IL-6/IL-6Rα-gp130 interaction via site III but only weak binding via site II. Collectively, our findings suggest a pathway for the evolution of the hexameric, IL-6/IL-6Rα/gp130 signaling complex and strategies for therapeutic targeting. We propose that the signaling complex originally involved specific interactions between IL-6 and IL-6Rα (site I) and between the D1 domain of gp130 and IL-6/IL-6Rα (site III), with the later inclusion of interactions between the D2 and D3 domains of gp130 and IL-6/IL-6Rα (site II) through serendipity. It seems likely that IL-6 signaling benefited from the evolution of a multipurpose, nonspecific protein interaction surface on gp130, now known as the cytokine binding homology region (site II contact surface), which fortuitously contributes to stabilization of the IL-6/IL-6Rα/gp130 signaling complex. |
| |
Keywords: | Cytokine NMR Protein Complexes Structural Biology Surface Plasmon Resonance (SPR) |
|
|