Most S100 proteins consist of two identical polypeptides (homodimeric), which are held together by noncovalent bonds. They are structurally similar to calmodulin. They differ from calmodulin, though, 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. In 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,[6] such as 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.[7]
Pathology
Several members of the S100 protein family are useful as markers for certain tumors and epidermal differentiation. They can be found in melanomas,[8] 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.[9] S100 proteins have been used in the lab as cell markers for anatomic pathology.
^Marenholz I, Heizmann CW, Fritz G (2004). "S100 proteins in mouse and man: from evolution to function and pathology (including an update of the nomenclature)". Biochemical and Biophysical Research Communications. 322 (4): 1111–22. doi:10.1016/j.bbrc.2004.07.096. PMID15336958.
^Wilson, AJ; Maddox, PH; Jenkins, D (January 1991). "CD1a and S100 antigen expression in skin Langerhans cells in patients with breast cancer". The Journal of Pathology. 163 (1): 25–30. doi:10.1002/path.1711630106. PMID2002421. S2CID70911084.
^Coppola D, Fu L, Nicosia SV, Kounelis S, Jones M (1998). "Prognostic significance of p53, bcl-2, vimentin, and S100 protein-positive Langerhans cells in endometrial carcinoma". Human Pathology. 29 (5): 455–62. doi:10.1016/s0046-8177(98)90060-0. PMID9596268.
^Shinzato M, Shamoto M, Hosokawa S, Kaneko C, Osada A, Shimizu M, Yoshida A (1995). "Differentiation of Langerhans cells from interdigitating cells using CD1a and S-100 protein antibodies". Biotechnic & Histochemistry. 70 (3): 114–8. doi:10.3109/10520299509108327. PMID7548432.
^Nonaka D, Chiriboga L, Rubin BP (2008). "Differential expression of S100 protein subtypes in malignant melanoma, and benign and malignant peripheral nerve sheath tumors". Journal of Cutaneous Pathology. 35 (11): 1014–9. doi:10.1111/j.1600-0560.2007.00953.x. PMID18547346. S2CID22907221.
^Penumutchu, Srinivasa R.; Chou, Ruey-Hwang; Yu, Chin (2014-10-17). "Interaction between S100P and the anti-allergy drug cromolyn". Biochemical and Biophysical Research Communications. 454 (3): 404–409. doi:10.1016/j.bbrc.2014.10.048. ISSN1090-2104. PMID25450399.