Fferences ?(rmsd less than 0.8 A for all Ca atoms). The structurally similar two lobes were in trans conformation about the axis of the central helix (Figures 2 and 3). A close examination of the current ligand-free CaM structure with previously reported CaM complexes showed that residues Ala74-Asp79 of the central helix (aa 65?2) are unwound, and bent by ,90u near Arg75; this reoriented the C-lobe in a perpendicular direction to the central helix (Figure 1 and 2). While a transformation of a-helix to loops has been previously reported [13,14], the kink observed at Arg75 is unique. This unique structure of 1531364 CaM represents one of its many possible conformations. The side chain of Arg75 is exposed on the surface of the molecule, which makes four hydrogen bonding contacts only withsymmetry-related Alprenolol web molecules (Arg38 and Arg127). The B-Title Loaded From File factors are the indicators of ordered nature of the atoms. The average B?factors for Arg75 of chain A and B are 47.5 and 50.9 A2, respectively. These average values are in good agreement with the B factors of the neighbouring residues, and suggest that Arg75 is well ordered (Figure 1). A detailed study of Lys76 mutation on CaM conformation was carried out by Medvedeva et al. [33]. A double mutation, containing a KGK insertion between residues 81 and 82, and a point mutation of K76P, makes the central helix highly flexible in Ca2+/CaM, as determined by the trypsinolysis [33]. Two mutants (K76P and K76E) were regarded as having a distorted central helix, and showed high resistance to trypsinolysis in the absence of Ca2+ [33]. Mutants K76A and K76V, on the other hand, decreased the rate of trypsinolysis of the central helix with a simultaneous increase in the rate of trypsinolysis in the Cterminal domain of CaM [33]. These studies revealed that various mutations in the central helix alter the conformation of CaM and confirm the highly flexible nature of the central helix, as observed through NMR studies [17]. Previously, a closed, compact crystal structure of CaM (PDB ?1PRW) was reported at 1.7 A resolution [34]. In this structure, CaM existed in a compact ellipsoidal conformation and revealed a sharp bend in the central helix. The two lobes were in cis orientation, in contrast to the trans orientation observed in theA Novel Conformation of CalmodulinFigure 2. Comparison among various calmodulin (CaM) structures. A: The Ca superposition of the present study novel trans conformation of CaM with several extended (trans) CaM conformations: 1PRW 1662274 (magenta), 2F2P (white), 2W73 (red), and 3CLN (dark salmon). B: The Ca superposition of present study novel trans conformation of CaM with several wrapped (cis) CaM conformations: 2BE6 (yellow), 2F3Y (light blue), 2O60 (pale green), 2VAY (teal), 2X0G (orange), 3BXK (deep purple), 3DVE (gray), 1CDM (olive). CaM conformations can be classified as “wrapped” and “extended”. In “wrapped” conformation, the two lobes are close to each others in cis orientation. In “extended” conformation, the two lobes are widely separated in trans orientations. In the present study, CaM adopted a novel trans conformation. The positions of metal ions in the current structure (blue) are labeled as Ca2+ (Green) and Zn2+ (grey). These structure alignments were carried out in PyMol [30]. doi:10.1371/journal.pone.0054834.gcurrent study. The N-lobe and C-lobe were close to each other and made several inter-domain contacts (Figure 3). The residues Asp79-Ser82 were unwound and made a type 1 reverse tu.Fferences ?(rmsd less than 0.8 A for all Ca atoms). The structurally similar two lobes were in trans conformation about the axis of the central helix (Figures 2 and 3). A close examination of the current ligand-free CaM structure with previously reported CaM complexes showed that residues Ala74-Asp79 of the central helix (aa 65?2) are unwound, and bent by ,90u near Arg75; this reoriented the C-lobe in a perpendicular direction to the central helix (Figure 1 and 2). While a transformation of a-helix to loops has been previously reported [13,14], the kink observed at Arg75 is unique. This unique structure of 1531364 CaM represents one of its many possible conformations. The side chain of Arg75 is exposed on the surface of the molecule, which makes four hydrogen bonding contacts only withsymmetry-related molecules (Arg38 and Arg127). The B-factors are the indicators of ordered nature of the atoms. The average B?factors for Arg75 of chain A and B are 47.5 and 50.9 A2, respectively. These average values are in good agreement with the B factors of the neighbouring residues, and suggest that Arg75 is well ordered (Figure 1). A detailed study of Lys76 mutation on CaM conformation was carried out by Medvedeva et al. [33]. A double mutation, containing a KGK insertion between residues 81 and 82, and a point mutation of K76P, makes the central helix highly flexible in Ca2+/CaM, as determined by the trypsinolysis [33]. Two mutants (K76P and K76E) were regarded as having a distorted central helix, and showed high resistance to trypsinolysis in the absence of Ca2+ [33]. Mutants K76A and K76V, on the other hand, decreased the rate of trypsinolysis of the central helix with a simultaneous increase in the rate of trypsinolysis in the Cterminal domain of CaM [33]. These studies revealed that various mutations in the central helix alter the conformation of CaM and confirm the highly flexible nature of the central helix, as observed through NMR studies [17]. Previously, a closed, compact crystal structure of CaM (PDB ?1PRW) was reported at 1.7 A resolution [34]. In this structure, CaM existed in a compact ellipsoidal conformation and revealed a sharp bend in the central helix. The two lobes were in cis orientation, in contrast to the trans orientation observed in theA Novel Conformation of CalmodulinFigure 2. Comparison among various calmodulin (CaM) structures. A: The Ca superposition of the present study novel trans conformation of CaM with several extended (trans) CaM conformations: 1PRW 1662274 (magenta), 2F2P (white), 2W73 (red), and 3CLN (dark salmon). B: The Ca superposition of present study novel trans conformation of CaM with several wrapped (cis) CaM conformations: 2BE6 (yellow), 2F3Y (light blue), 2O60 (pale green), 2VAY (teal), 2X0G (orange), 3BXK (deep purple), 3DVE (gray), 1CDM (olive). CaM conformations can be classified as “wrapped” and “extended”. In “wrapped” conformation, the two lobes are close to each others in cis orientation. In “extended” conformation, the two lobes are widely separated in trans orientations. In the present study, CaM adopted a novel trans conformation. The positions of metal ions in the current structure (blue) are labeled as Ca2+ (Green) and Zn2+ (grey). These structure alignments were carried out in PyMol [30]. doi:10.1371/journal.pone.0054834.gcurrent study. The N-lobe and C-lobe were close to each other and made several inter-domain contacts (Figure 3). The residues Asp79-Ser82 were unwound and made a type 1 reverse tu.
