The dimerization interface of the metastasis-associated protein S100A4 (Mts1): in vivo and in vitro studies.
The S100 calcium-binding proteins are implicated in signal transduction, motility, and cytoskeletal dynamics. The three-dimensional structure of several S100 proteins revealed that the proteins form non-covalent dimers. However, the mechanism of the S100 dimerization is still obscure. In this study we characterized the dimerization of S100A4 (also named Mts1) in vitro and in vivo. Analytical ultracentrifugation revealed that apoS100A4 was present in solution as a mixture of monomers and dimers in a rapidly reversible equilibrium (K(d) = 4 +/- 2 microm). The binding of calcium promoted dimerization. Replacement of Tyr-75 by Phe resulted in the stabilization of the dimer. Helix IV is known to form the major part of the dimerization interface in homologous S100 proteins. By using the yeast two-hybrid system we showed that only a few residues of helix IV, namely Phe-72, Tyr-75, Phe-78, and Leu-79, are essential for dimerization in vivo. A homology model demonstrated that these residues form a hydrophobic cluster on helix IV. Their role is to stabilize the structure of individual subunits rather than provide specific interactions across the dimerization surface. Our mutation data showed that the specificity at the dimerization surface is not particularly stringent, which is consistent with recent data indicating that S100 proteins can form heterodimers.
Department of Molecular Cancer Biology, Danish Cancer Society, Copenhagen DK-2100, Denmark.
S
S
Tarabykina
D J
DJ
Scott
P
P
Herzyk
T J
TJ
Hill
J R
JR
Tame
M
M
Kriajevska
D
D
Lafitte
P J
PJ
Derrick
G G
GG
Dodson
N J
NJ
Maitland
E M
EM
Lukanidin
I B
IB
Bronstein
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004252:DNA Mutational Analysis; D019281:Dimerization; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins / Q000737:chemistry* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D014461:Ultracentrifugation
D000071999:S100 Calcium-Binding Protein A4; D009418:S100 Proteins; C077591:S100A4 protein, human