title: Molecular mechanisms of pharmaceutical drug binding  into calsequestrin.
abstract: Calsequestrin (CASQ) is a major Ca2+-storage/buffer protein present in the sarcoplasmic reticulum of both skeletal (CASQ1) and cardiac (CASQ2) muscles. CASQ has significant affinity for a number of pharmaceutical drugs with known muscular toxicities. Our approach, with in silico molecular docking, single crystal X-ray diffraction, and isothermal titration calorimetry (ITC), identified three distinct binding pockets on the surface of CASQ2, which overlap with 2-methyl-2,4-pentanediol (MPD) binding sites observed in the crystal structure. Those three receptor sites based on canine CASQ1 crystal structure gave a high correlation (R2 = 0.80) to our ITC data. Daunomycin, doxorubicin, thioridazine, and trifluoperazine showed strong affinity to the S1 site, which is a central cavity formed between three domains of CASQ2. Some of the moderate-affinity drugs and some high-affinity drugs like amlodipine and verapamil displayed their binding into S2 sites, which are the thioredoxin-like fold present in each CASQ domain. Docking predictions combined with dissociation constants imply that presence of large aromatic cores and less flexible functional groups determines the strength of binding affinity to CASQ. In addition, the predicted binding pockets for both caffeine and epigallocatechin overlapped with the S1 and S2 sites, suggesting competitive inhibition by these natural compounds as a plausible explanation for their antagonistic effects on cardiotoxic side effects.
authors.affiliation: Department of Chemistry, Washington State University, Pullman, WA 99164-4630, USA. chkang@wsu.edu.
authors.forename: Arun K
authors.initials: AK
authors.lastname: Subra
authors.forename: Mark S
authors.initials: MS
authors.lastname: Nissen
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Lewis
authors.forename: Ashwin K
authors.initials: AK
authors.lastname: Muralidharan
authors.forename: Emiliano J
authors.initials: EJ
authors.lastname: Sanchez
authors.forename: Hendrik
authors.initials: H
authors.lastname: Milting
authors.forename: Chul Hee
authors.initials: CH
authors.lastname: Kang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002155:Calsequestrin / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D062105:Molecular Docking Simulation; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D004364:Pharmaceutical Preparations / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D011789:Quantum Theory; D011817:Rabbits
chemical_list: D002155:Calsequestrin; D008024:Ligands; D004364:Pharmaceutical Preparations