Fig. 3. Homology model and schematic diagram of mutated C. elegans calsequestrin. (A) Schematic prediction of polymerized CSQ-1. The monomeric model of CSQ-1 was built using the rabbit calsequestrin structure. The tetramer is shown as C-traces to display putative polymerizing interactions between monomers. Monomers are either green or yellow. N and C-termini of each molecule are shown as dashed lines because they are disordered in the template structure. Note the positively charged residues in the C-terminus specific to C. elegans calsequestrins. The location of the conserved back-to-back interface formed between SAH (Serine Acidic Hydrophbic) and DBH (Dibasic Hydrophobic) is boxed in red. Lys111 residues are shown as spheres. (B) Close-up view of the back-to-back interface of CSQ-1. The two interacting molecules are green and yellow. Three negatively charged residues (Glu247, Glu251 and Asp196) are placed in the vicinity of Lys111 and might participate in a salt bridge. (C) Amino acid sequence of C. elegans calsequestrin aligned with the rabbit skeletal calsequestrin and human cardiac calsequestrin CSQ2 amino acid sequences. Green box, signal sequence; first to fourth red and first and second yellow boxes indicate C26 and C17, N23-31, N32-43, DBH, SAH, respectively. (D) Each DNA construct represents wild-type (WT), N-terminal 9-amino-acid truncation, N-terminal 12-amino-acid truncation, C-terminal 17-amino-acid truncation and C-terminal 26-amino-acid truncation. Mutant CSQ-1 constructs K111A and Bedouin contain a Lys111 to Ala and Asp318 to His mutation, respectively. These constructs were introduced into the csq-1(jh109) mutant and their expression was detected by western blotting using anti-CSQ-1 and anti-PYP-1 (internal control) antibodies.