S100A4 (also metastasin, Mtsl and calvasculin) is an 11 kD member of the S100 (soluble in 100% saturated ammonium sulfate) family of proteins (1-5). The S100 family is a 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 α-helices (helix E and helix F) that were originally identified in a right-handed model of carp muscle calcium-binding protein (6). Mouse 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). Mouse S100A4 shares 93%, 96% and 89% aa identity with human, rat and dog S100A4, respectively. S100A4 exists as 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 β1 (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).||Source: A DNA sequence encoding mouse S100-A4 (Met 1-Lys 101; Accession # NP_03544) with a C-terminal 6X histidine tag was expressed in E. coli.||Molecular Mass: The non-methionyl form of recombinant human S100-A4 contains 106 amino acids and has a predicted molecular mass of 12.4 kD.||Endotoxin Level: < 1.0 EU per 1 μg of the protein as determined by the LAL method.||Activity: Measured by its ability to induce neurite outgrowth from E13 chick dorsal root ganglia neurons. Immobilized rhS100A4 (at a 3 μL droplet containing 90 ng) on nitrocellulose-coated microplate is sufficient to significantly enhance neurite outgrowth.||Reconstitution: It is recommended that sterile PBS be added to the vial to prepare a working stock solution of no less than 100ug/ml. The carrier-free protein should be used immediately upon reconstitution to avoid losses in activity due to non-specific binding to the inside surface of the vial. For long term storage as a dilute solution, a carrier protein (e.g. 0.1% HSA or BSA) should be added to the vial.||Storage and Stability: Lyophilized samples are stable for up to twelve months at -20°C. Upon reconstitution, this protein, in the presence of a carrier protein, can be stored under sterile conditions at 2°-8° C for one month or at -20°C in a manual defrost freezer for three months without detectable loss of activity. Avoid repeated freeze-thaw cycles.

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