S-100A13: S-100A13 domain found in proteins similar to S100A13. S100A13 is a calcium-binding protein belonging to a large S100 vertebrate-specific protein family within the EF-hand superfamily of calcium-binding proteins. Note that the S-100 hierarchy, to which this S-100A13 group belongs, contains only S-100 EF-hand domains, other EF-hands have been modeled separately. S100A13 is involved in the cellular export of interleukin-1 (IL-1) and of fibroblast growth factor-1 (FGF-1), which plays an important role in angiogenesis and tissue regeneration. Export is based on the CuII-dependent formation of multiprotein complexes containing the S100A13 protein. Assembly of these complexes occurs near the inner surface of the plasma membrane. Binding of two Ca(II) ions per monomer triggers key conformational changes leading to the creation of two identical and symmetrical Cu(II)-binding sites on the surface of the protein, close to the interface between the two monomers. These Cu(II)-binding sites are unique among the S100 proteins, which are reported to bind Cu(II) or Zn(II) ions in addition to Ca(II) ions. In addition, the three-dimensional structure of S100A13 differs significantly from those of other S100 proteins; the hydrophobic pocket that largely contributes to protein-protein interactions in other S100 proteins is absent in S100A13. The structure of S100A13 contains a large patch of negatively charged residues flanked by dense cationic clusters, formed mostly from positively charged residues from the C-terminal end, which plays major role in binding FGF-1.
Comment:the N-terminal EF hand is a S100 specific feature while the C-terminal canonical EF hand is similar to the EF hands in calmodulin, troponin C, and parvalbumin
Comment:the second binding site (C-terminal EF hand) has a greater affinity for Ca2+ than the first (N-terminal EF hand)
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