Antibodies to S100 Family - FocusOn 041

Introduction: One of the largest subfamilies of EF-hand Ca2+-binding proteins is constituted by the S100 proteins. They comprise different human members which display a diverse pattern of cell- and tissue-specific distribution consistent with their pleiotropic intra- and extracellular functions. These functions are brought about through interaction with diverse target proteins, probably sometimes in a concerted manner with the ubiquitously expressed calmodulin.

A wide range of diseases, including cardiomyopathies, neurological diseases, chronic inflammation, and cancer were recently linked to deregulation of S100 gene expression. Hence, S100 proteins are currently considered for their potential use in clinical diagnostics as well as for therapeutic interventions.

Protein Structure and Biochemical Properties

S100 proteins are characterized by two distinct EF-hand calcium-binding motifs with different affinities. Usually, the carboxy-terminal EF-hand is referred to as the canonical Ca2+-binding loop with a rather high affinity, whereas the amino-terminal loop is S100 specific and displays lower Ca2+-binding affinity. These EF-hands are flanked by hydrophobic regions, responsible for interaction with target proteins, and separated by a central hinge region. Generally, S100 proteins can form homo- or heterodimers and bind 4 Ca2+ per dimer. Several S100 proteins also bind Zn2+, however to a different site. Zn2+-binding is able to modify the Ca2+ affinity in a few cases. Furthermore, S100B and S100A5 also bind Cu2+. S100A7 differs from the other S100 proteins of known structure in its lack of calcium binding ability in one EF-hand at the N-terminus. This protein is markedly over-expressed in the skin lesions of psoriatic patients, but is excluded as a candidate gene for familial psoriasis susceptibility. Therefore, there is considerable variation in the biochemical and metal-binding properties of S100 proteins the physiological consequences of which remain to be investigated.

Biological Functions

S100 proteins are involved in a large number of cellular activites such as signal transduction, cell differentiation, regulation of cell motility, transcription and cell cycle progression which are brought about through modulation of target proteins in a Ca2+-, and possibly also in a Zn2+- and Cu2+-dependent manner. In general, one can distinguish intracellular functions of S100 proteins such as regulation of protein phosphorylation, cytoskeletal assembly, transcription or enzyme activities from extracellular functions. These extracellular functions include chemotactic activity (S100A8 and S100A9) as well as neurotrophic acitivities (S100B). However, the mechanisms of secretion as well as the nature of high affinity surface receptors are largely unknown. One good candidate for such a receptor might be the receptor for advanced glycosylation end-products (RAGE) which was recently shown to bind S100B and S100A12.

Antibody Tools for the Detection of S100 Proteins

During the last years interest in antibodies to proteins of the S100 family increased dramatically. Therefore, more and more antibodies were added to our product list and the antibody panel grew to one of the largest collections of antibodies to S100 Proteins. Clone 27E10 is unique in that it recognizes an epitope on the MRP8/14 (S100A8/S100A9) heterocomplex also called Calprotectin that is not exposed on the individual subunits MRP8 or MRP14. The antibody reacts with human subpopulations of macrophages, monocytes and granulocytes and is very useful tool as human macrophage marker. Nearly all antibodies can be used for Western blotting, many of them are suitable for immunohistochemistry procedures and/or ELISA techniques.

Fig.1: Cat.-No. AM10018PU-N S100A1 antibody staining of Formalin-Fixed and Paraffin-Embedded Human neurofibroma tissue (4 μm) show positive immunostaining of tumor cells and peripheral nerve.

Fig.2: Cat.-No. AM10018PU-N S100A1 antibody staining of Formalin-Fixed and Paraffin-Embedded skin melanoma tissue (4 μm) show positive immunostaining of melanoma cells.

Fig.3: Cat.-No. AM10018PU-N S100A1 antibody staining of Formalin-Fixed and Paraffin-Embedded Human breast tissue (4 μm) show positive immunostaining of the outer myoepithelial cell component in mammary lobule.

Fig.4: Cat.-No. SP2091P S100 antibody staining of Formalin Fixed, Paraffin Human melanoma processed tissue.

Fig.5: Immunofluorescence using Cat.-No. AP21316PU-N S100A10 antibody in Rat choroid plexus and FITC-conjugated Donkey anti-Chicken secondary antibodies.

Fig.6: Cat.-No. AP12456PU-N S100A11 antibody staining of Formalin-Fixed, Paraffin-Embedded Human breast carcinoma tissue using peroxidase-conjugated secondary antibody, followed by DAB staining. This data demonstrates the use of this antibody for Immunohistochemistry. Clinical relevance has not been evaluated.

Fig.7: Cat.-No. AM08370PU-N S100A7 antibody staining of Formalin-Fixed Paraffin-Embedded Human Skin at 10 µg/ml followed by biotinylated anti-Mouse IgG secondary antibody, Alkaline Phosphatase-Streptavidin and Chromogen.

Fig.8: Cat.-No. AP00589PU-N S100A4 antibody staining of Formalin-Fixed, Paraffin-Embedded Human melanoma using AEC chromogen. Note cytoplasmic staining of tumor cells.

Fig.9: Cat.-No. AP00590PU-N S100A6 antibody staining of Formalin-Fixed, Paraffin-Embedded Human tonsil using peroxidase-conjugate and AEC chromogen. Note cytoplasmic staining of cells in germinal center.

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