Calcium-dependent tetramer formation of S100A8 and S100A9 is essential for biological activity.
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.
Leukert
Nadja
N
Institute of Experimental Dermatology, University of Muenster, Roentgenstr. 21, 48149 Muenster, Germany.
Vogl
Thomas
T
Strupat
Kerstin
K
Reichelt
Rudolf
R
Sorg
Clemens
C
Roth
Johannes
J
D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D040501:Calgranulin A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D040502:Calgranulin B / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D019281:Dimerization; D020832:EF Hand Motifs; D006801:Humans; D009154:Mutation; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014404:Tubulin / Q000378:metabolism
D040501:Calgranulin A; D040502:Calgranulin B; D011994:Recombinant Proteins; D014404:Tubulin; D002118:Calcium