STRUCTURE-FUNCTION ANALYSIS OF THE C-TERMINAL SEGMENT OF HUMAN INTERLEUKIN-6

Citation
Xm. Li et al., STRUCTURE-FUNCTION ANALYSIS OF THE C-TERMINAL SEGMENT OF HUMAN INTERLEUKIN-6, The Journal of biological chemistry, 268(30), 1993, pp. 22377-22384
Citations number
42
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
268
Issue
30
Year of publication
1993
Pages
22377 - 22384
Database
ISI
SICI code
0021-9258(1993)268:30<22377:SAOTCS>2.0.ZU;2-I
Abstract
It has been hypothesized that interleukin-6 (IL-6) and granulocyte-col ony-stimulating factor (G-CSF) may fold as four-alpha-helix bundle pro teins. To probe the functional role of the putative fourth helical seg ment of IL-6 (D-helix), a chimeric IL-6/G-CSF analog containing the pr edicted D-helix of G-CSF as well as a panel of IL-6 D-helix point muta nts were analyzed for their respective secondary structure, antigenici ty, and receptor binding and biological activities. The putative D-hel ix of IL-6 could not be replaced by its G-CSF counterpart in spite of their high degree of similarity and thus is indispensable for the anti genic and functional integrity of the IL-6 receptor binding site. Conv ersely, the grafting of the G-CSF D-helix did not confer any G-CSF act ivity to IL-6. A synthetic helical peptide containing the IL-6 D-helix was inactive, even when mixed with or linked to a peptide from the A- helix known to be involved in the active site. However, the conserved residues F173, R179, and R182 found in the D-helices of both IL-6 and G-CSF critically contribute to the architecture of the IL-6 active sit e. Indeed, mutation of F173 or R179 markedly affected IL-6 receptor bi nding and biological activities, but not the conformation of a major n eutralization epitope. Furthermore, substitution of R182 resulted in a significant unfolding of the D-helix accompanied by a drastic loss in IL-6 antigenicity and functional activities. Nevertheless, residues o ther than F173, R179, and R182 also contribute to IL-6 specificity.