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Figure 3 | Genome Biology

Figure 3

From: The calpains: modular designs and functional diversity

Figure 3

Structures of calpain modules and calpain-2. (a) Ribbon diagram of the structure of the penta-EF-hand module (domain dVI) of Cpns-1 from pig. It is shown here as a homodimer (one chain green, one cyan). The short helical peptides (yellow and magenta) are 19-residue mimics of the conserved C peptide of the calpain inhibitor calpastatin bound to dVI in the presence of calcium (orange spheres). The structure is from PDB 1NX1 (Todd et al. [19]). (b) Ribbon diagram of the structure of the rat calpain-2 heterodimer. The catalytic core domains (dI-dII) are in light and dark blue, respectively. Catalytic residues are shown as magenta sticks (with the engineered mutation of C105S) and the arrow designates the active-site cleft between domains dI and dII. Domain dIII (brown) is C2-like. The penta-EF-hand domain dIV of the large subunit (Capn-2) is in yellow, and the similar domain dVI of the small subunit (Cpns-1) is in orange. Domain dV, the amino-terminal glycine-rich region of the small subunit, was truncated by protein engineering; in the human enzyme it is highly flexible and structurally unresolved [21]. The amino-terminal helix and linker loops are in green. The structure is from PDB 1DF0 (Hosfield et al. [20]). The dVI heterodimer in (a) is very similar to that formed between the dIV and dVI domains, and can be used to model this interaction. (c) Ribbon diagram of the structure of the calcium-bound catalytic core (domains dI-dII) of rat calpain-1 based on PDB 1TL9 (Moldoveanu et al. [26]). The bound inhibitor leupeptin is shown as gold, blue and red spheres; the magenta spheres are two calcium ions bound to hitherto unknown sites. All ribbon diagrams were generated using PyMol (DeLano Scientific, Palo Alto, CA, USA).

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