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S100A1, also known as S100 calcium-binding protein A1 is a protein which in humans is encoded by the ''S100A1'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=6271 )〕 S100A1 is highly expressed in cardiac and skeletal muscle, and localizes to Z-discs and sarcoplasmic reticulum. S100A1 has shown great promise as an effective candidate for gene therapy to treat post-myocardially infarcted cardiac tissue. == Structure == S100A1 is a member of the S100 family of proteins expressed in cardiac muscle, skeletal muscle and brain, with highest density at Z-lines and sarcoplasmic reticulum. S100A1 contains 4 EF-hand calcium-binding motifs in its dimerized form, and can exist as either a hetero or homodimer. The S100A1 homodimer is high affinity (nanomolar range or tighter), and is formed through hydrophobic packing of an X-type 4-helix bundle created between helices 1, 1', 4, and 4'. Protein nuclear magnetic resonance spectroscopy structural information on the homodimeric form of this protein shows that each monomer is helical and contains two EF-hand calcium-binding loops; one in the N-terminus and a canonical EF hand in the C-terminus having higher calcium affinity (dissociation constant of roughly 20 micromolar). The two EF hand domains neighbor each other in three dimensional space, and are connected to each other through a short beta sheet region (residues 27–29 and 68–70). Upon binding calcium, helix 3 of S100A1 re-orients from being relatively antiparallel to helix 4 to being roughly perpendicular. This conformational change is different from most EF hands, in that the entering helix, and not the exiting helix, moves. This conformational change exposes a large hydrophobic pocket between helix 3, 4, and the hinge region of S100A1 that is involved in virtually all calcium-dependent target protein interactions. These biophysical properties seem to be well conserved across the S100 family of proteins. Helix 3, 4, and the hinge region are the most divergent areas between individual S100 proteins, and so it is likely that the sequence of these regions is pivotal in fine-tuning calcium-dependent target binding by S100 proteins. Interestingly, S-Nitrosylation of S100A1 at Cys85 reorganizes the conformation of S100A1 at the C-terminal helix and the linker connecting the two EF hand domains. The most accurate high-resolution solution structure of human apo-S100A1 protein (PDB accession code: 2L0P) has been determined by means of NMR spectroscopy in 2011. S100 genes include at least 19 members which are located as a cluster on chromosome 1q21. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「S100A1」の詳細全文を読む スポンサード リンク
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