Recombinant Human S100A4 Protein, CF

S100A4 (also metastasin, Mtsl and calvasculin) is an 11 kDa member of the S100 (soluble in 100% saturated ammonium sulfate) family of proteins (1 - 5). The S100 family is further classified as a member of the EF-hand superfamily of Ca⁺⁺-binding proteins. These participate in both calcium-dependent and calcium-independent protein-protein interactions. The hallmark of this superfamily is the EF-hand motif that consists of a Ca⁺⁺-binding site flanked by two alpha-helices (helix E and helix F) that were originally identified in a right-handed model of carp muscle calcium-binding protein (6). Human S100A4 is 101 amino acids (aa) in length (1, 2). It contains two EF hand domains, one between aa 12 - 47, and a second between aa 50 - 85. The first domain has a 14 aa cation-binding motif and binds Ca⁺⁺ with low affinity. The second Ca⁺⁺-binding motif is 12 aa in length and binds Ca⁺⁺ with high affinity. S100A4 has no classical signal sequence but is secreted from cells (3, 7). Human S100A4 shares 93% and 95% aa identity with mouse and canine S100A4, respectively. S100A4 reportedly exists as a dimer (8, 9, 10). Extracellular S100A4 is reported to induce MMP production, activate MMPs, promote neurite outgrowth and stimulate cardiomyocyte proliferation (4, 10, 11, 12, 13). Within the cell, dimers are likely the functional unit. Here, they are constitutive homo- or heterodimers (with S100A1) that interact with Ca⁺⁺, undergo a conformational change, and subsequently bind to cytoplasmic targets. Known targets include p53, myosin heavy chain II, F-actin and liprin beta1 (4, 14). In general, it can be said that S100A4 blocks target phosphorylation and multimerization (4, 7, 14). S100A4 activity has been associated with cell transformation. It seems likely this is either coincidental, or a consequence, rather than a cause of transformation (3).