Drug Binding by Calmodulin: Crystal Structure of a Calmodulin-Trifluoperazine Complex

Abstract

The crystal structure of calmodulin (CaM) bound to trifluoperazine (TFP) has been determined and refined to a resolution of 2.45 A. Only one TFP is bound to CaM, but that is sufficient to cause distortion of the central alpha-helix and juxtaposition of the N- and C-terminal domains similar to that seen in CaM-polypeptide complexes. The drug makes extensive contacts with residues in the C-terminal domain of CaM but only a few contacts with one residue in the N-terminal domain. The structure suggests that substrate binding to the C-terminal domain is sufficient to cause the conformational changes in calmodulin that lead to activation of its targets.

Phenothiazines inhibit S100A4 function by inducing protein oligomerization

“…For example, troponin C binds two TFP molecules (PDB 1WRK) and calmodulin binds TFP with a range of stoichiometries; 1∶1 (PDB 1CTR), 1∶2 (PDB 1A29), and 1∶4 (PDB 1LIN) (28)(29)(30). Even though S100A4, troponin C, and calmodulin are built upon the same basic four-helical structural module, the architectures of the TFP binding pockets, and the positions and orientations of the bound TFP molecules are quite different amongst the three proteins (Fig.…”

Locking Regulatory Myosin in the Off-state with Trifluoperazine

“…There is a monotonic decline in actinactivated MgATPase (ϮCa 2ϩ ) that is complete at 300 M TFP, and prior removal of R-LC by EDTA still permits TFP inactivation of the desensitized myosin and exhibits the same concentration dependence (Fig. 3), suggesting that the heavy chain⅐E-LC complex can be induced to attain this extreme (12), as seen from the same perspective as for calmodulin (a); c, relationship of the putative TFP-binding site within E-LC as found within the smooth muscle myosin motor domain⅐E-LC ADP⅐AlF 4 Ϫ complex (35), illustrating its proximity to heavy-chain amino acid residues at the entrance to the nucleotide-binding pocket; d, relationship of the putative TFP-binding site within E-LC as found within scallop adductor myosin MgADP⅐S-1 (36), illustrating its proximity to heavy-chain amino acid residues within the SH3 domain. In c and d, perspectives were chosen to illustrate the proximity of the E-LC C-terminal TFP-binding lobe to key heavy-chain surface features; the view of the converter region, which maintains its relationship to E-LC in both structures (35), is approximately the same in both cases.…”

“…6). In the stoichiometric TFP⅐calmodulin complex, the hydrophobic tricyclic ring of TFP localizes to a hydrophobic pocket within the C-terminal lobe of calmodulin, entrapping TFP⅐calmodulin in the same conformation as that seen when calmodulin binds to a target peptide substrate (4,6,7). Although the C-terminal lobes of scallop R-LC and E-LC exhibit semi-open conformations, in contrast to the C-terminal lobe of calmodulin, which displays a fully open conformation (10), the required hydrophobic pocket remains available, albeit less deeply placed (Fig.…”

“…The structure of the TFP⅐calmodulin complex in the presence of calcium has been determined at 2.45-Å resolution (4,5), where it was shown that TFP induces a profound conformational change in calmodulin, converting the elongated dumbbell to a compact globular structure, analogous to the form obtained through the binding of calmodulin to a target peptide (6,7). This effect was accomplished when a single TFP molecule bound to the predominant binding site, a hydrophobic pocket within the C-terminal domain (4). Additional TFP-binding sites are apparent when the TFP concentration is raised (5).…”

HMN-709, a Chlorobenzenesulfonamide Derivative, Is a New Membrane-Permeable Calmodulin Antagonist

“…In addition, a set of CaM antagonists including W-7 and W-9 has been generated from naphthalenesulfonamide derivatives (14). The recent elucidation of the crystal structure of the Ca 2+/CaM complex with trifluoperazine revealed that Ca 2+/CaM binds to the CaM antagonist in a similar shape to that observed in Ca 2+/CaM/M13 (9,15). Pharmacological studies by Hidaka and co-workers suggest that CaM is involved in platelet aggregation and secretion (16), vascular contraction (17), cell proliferation (18) and the degranulation of neutrophils (19).…”