Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 359, Issue 4, Pages 961-972Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2006.04.009
Keywords
tetramerization; S100 proteins; calcium-binding; tubulin polymerization; EF-hand mutants
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S100 proteins comprise the largest family of calcium-binding proteins. Members of this family usually form homo- or heterodimers, which may associate to higher-order oligomers in a calcium-dependent manner. The heterodimers of S100A8 and S100A9 represent the major calcium-binding proteins in phagocytes. Both proteins regulate migration of these cells via modulation of tubulin polymerization. Calcium binding induces formation of (S100A8/S100A9)(2) tetramers. The functional relevance of these higher-order oligomers of S100 proteins, however, is not yet clear. To investigate the importance of higher-order oligomerization for S100 proteins, we created a set of mutations within S100A9 (N69A, E78A, N69A + E78A) destroying the high-affinity C-terminal calcium-binding site (EF-hand II). Mutations in EF-hand II did not interfere with formation of the S100A8/S100A9 heterodimer as demonstrated by yeast two-hybrid experiments and pull-down assays. In contrast, mass spectrometric analysis and density gradient centrifugation revealed that calcium-induced association of (S100A8/S100A9)(2) tetramers was strictly dependent on a functional EF-hand II in S100A9. Failure of tetramer formation was associated with a lack of functional activity of S100A8/S100A9 complexes in promoting the formation of microtubules. Thus, our data demonstrate that calcium-dependent formation of (S100A8/S100A9)(2) tetramers is an essential prerequisite for biological function. This is the first report showing a functional relevance of calcium-induced higher-order oligomerization in the S100 family. (c) 2006 Elsevier Ltd. All rights reserved.
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