Figure 3.

Structural characterization of human and rat CALR. (A) X-ray crystal structure of the N-domain human of CALR (residues 18–204) and the N-terminal half of the C-domain (residues 303–368) connected by a GSG tripeptide (PDB ID: 3POW; Chouquet et al., 2011). The expected localization of MoRF1 (residues 170–176, in red), MoRF2 (residues 198–204, green), and MoRF4 (residues 304–352, ice-blue) in the crystal structure of the human protein is indicated. Note that in this construct, the P-domain is removed and replaced by the GSG tripeptide. With the exception to MoRFs that have their own color coding (see above), CALR structure is colored according to the secondary structure content, with β-strands, α-helices, 3₁₀ helices, β-turns, and irregular structure shown by yellow, purple, blue, cyan, and white colors, respectively. (B) Solution NMR structure of the P-domain of the rat CALR (residues 206–305 in UniProt ID: P18418) (PDB ID: 1HHN; Ellgaard et al., 2001b). NMR analysis generates an ensemble of structures, all of which are consistent with the observed experimental restraints. Shown here is a conformational ensemble representing structure of the P-domain, which is one of the regions removed from the construct used in the crystallization studies of the human protein (see Figure 3A). This conformational ensemble contains an overlay of 20 molecular models, each shown by its own color. A highly dynamic nature of the conformational ensemble describing structure of P-CALR is evidenced by the “fuzzy” appearance of the conformational ensemble describing its solution structure. (C) Solution NMR structure of one of the members of the P-domain dynamic conformational ensemble (model 1 in PDB ID: 1HHN; Ellgaard et al., 2001b). Position of MoRF3 (residues 259–269) is indicated in red. With the exption to this MoRF, structure of P-CALR is colored according to the secondary structure content, with β-strands, β-turns, and irregular structure shown by yellow, cyan, and white colors, respectively.