Most S100 proteins are homodimeric, consisting of two identical polypeptides, which are held together by non-covalent bonds. S100 proteins are structurally similar to calmodulin. On the other hand they differ from calmodulin on the other features. For instance, their expression pattern is cell-specific, i.e. they are expressed in particular cell types. Their expression depends on environmental factors. To contrast, calmodulin is a ubiquitous and universal intracellular Ca2+ receptor widely expressed in many cells.
S100 proteins have been implicated in a variety of intracellular and extracellular functions. S100 proteins are involved in regulation of protein phosphorylation, transcription factors, Ca2+ homeostasis, the dynamics of cytoskeleton constituents, enzyme activities, cell growth and differentiation, and the inflammatory response. S100A7 (psoriasin) and S100A15 have been found to act as cytokines in inflammation, particularly in autoimmune skin conditions such as psoriasis.
Several members of the S100 protein family are useful as markers for certain tumors and epidermal differentiation. It can be found in melanomas, 100% of schwannomas, 100% of neurofibromas (weaker than schwannomas), 50% of malignant peripheral nerve sheath tumors (may be weak and/or focal), paraganglioma stromal cells, histiocytoma and clear cell sarcomas. Further, S100 proteins are markers for inflammatory diseases and can mediate inflammation and act as antimicrobials.
^Marenholz I, Heizmann CW, Fritz G (October 2004). "S100 proteins in mouse and man: from evolution to function and pathology (including an update of the nomenclature)". Biochem. Biophys. Res. Commun.322 (4): 1111–22. doi:10.1016/j.bbrc.2004.07.096. PMID15336958.
^Nonaka D, Chiriboga L, Rubin BP (November 2008). "Differential expression of S100 protein subtypes in malignant melanoma, and benign and malignant peripheral nerve sheath tumors". J. Cutan. Pathol.35 (11): 1014–9. doi:10.1111/j.1600-0560.2007.00953.x. PMID18547346.
^Wolf R, Ruzicka T, Yuspa SH (July 2010). "Novel S100A7 (psoriasin)/S100A15 (koebnerisin) subfamily: highly homologous but distinct in regulation and function". Amino Acids41 (4): 789–96. doi:10.1007/s00726-010-0666-4. PMID20596736.
Wolf R, Voscopoulos CJ, FitzGerald PC et al. (2006). "The mouse S100A15 ortholog parallels genomic organization, structure, gene expression, and protein-processing pattern of the human S100A7/A15 subfamily during epidermal maturation". J. Invest. Dermatol.126 (7): 1600–8. doi:10.1038/sj.jid.5700210. PMID16528363.CS1 maint: Explicit use of et al. (link)
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Ronald Wolf, Francesca Mascia, Alif Dharamsi, O. M. Zack Howard, Christophe Cataisson, Val Bliskovski, Jason Winston, Lionel Feigenbaum, Ulrike Lichti, Thomas Ruzicka Triantafyllos Chavakis, and Stuart H. Yuspa. (2010). "Gene from a Psoriasis Susceptibility Locus Primes the Skin for Inflammation.". Science Translational Medicine2 (61): 61ra90. doi:10.1126/scitranslmed.3001108. PMID21148126.