English: Parvalbumins have six α-helices A-to-F and two “EF-hand” domains for binding Ca2+ ions (indicated as spheres). (A) The structure, in cartoon format, of common carp pvalb4_(Chr.A3) (a β2-parvalbumin; PDB accession 4CPV), which was the first parvalbumin of which the structure was elucidated. Different α-helices are in different colors. (B) Superimposition of various parvalbumin structures, in ribbon format, reveals a common structure. Light pink, human α-parvalbumin (1RK9); pink, pike pvalb7 α-parvalbumin (2PAS); magenta, spotless smooth-hound shark SPV-I α-parvalbumin (5ZGM); green, human oncomodulin (1TTX); splitpea green, chicken CPV3-oncomodulin (2KYF); soft purple, chicken ATH β2-parvalbumin (3FS7); cyan, Atlantic cod pvalb2 β2-parvalbumin (2MBX); green cyan, pike pvalb3 β2-parvalbumin (1PVB); aquamarine, common carp pvalb4_(Chr.A3) β2-parvalbumin (4CPV); light teal, spotless smooth-hound shark SPV-II β2-parvalbumin (5ZH6). (C) The structure, in ribbon format, of common carp pvalb4_(Chr.A3) (PDB accession 4CPV), shows in black those residues that are well conserved throughout EF-hand domain family molecules and in gray other residues that are well conserved throughout parvalbumins; the sidechains of these residues are shown in sticks format. This figure is used, with permission, from the open access article https://doi.org/10.3390/genes15101337, and the figures were created with the help of Pymol 2.5.2 software.