title: Inhibition of calcium-calmodulin complex formation by vasorelaxant basic dipeptides demonstrated by in vitro and in silico analyses.
abstract: BACKGROUND
  Tryptophan-histidine (Trp-His) was found to suppress the activity of the Ca²⁺/calmodulin (CaM)-dependent protein kinases II (CaMKII), which requires the Ca²⁺-CaM complex for an initial activation. In this study, we attempted to clarify whether Trp-His inhibits Ca²⁺-CaM complex formation, a CaMKII activator.
  
  
  METHODS
  The ability of Trp-His and other peptides to inhibit Ca²⁺-CaM complex formation was investigated by a Ca²⁺-encapsulation fluorescence assay. The peptide-CaM interactions were illustrated by molecular dynamic simulation.
  
  
  RESULTS
  We showed that Trp-His inhibited Ca²⁺-CaM complex formation with a 1:1 binding stoichiometry of the peptide to CaM, considering that Trp-His reduced Hill coefficient of Ca²⁺-CaM binding from 2.81 to 1.92. His-Trp also showed inhibitory activity, whereas Trp+His, 3-methyl His-Trp, and Phe-His did not show significant inhibitory activity, suggesting that the inhibitory activity was due to a peptide skeleton (irrespective of the sequence), a basic amino acid, a His residue, the N hydrogen atom of its imidazole ring, and Trp residue. In silico studies suggested the possibility that Trp-His and His-Trp interacted with the Ca²⁺-binding site of CaM by forming hydrogen bonds with key Ca²⁺-binding residues of CaM, with a binding free energy of -49.1 and -68.0 kJ/mol, respectively.
  
  
  CONCLUSIONS
  This is the first study demonstrating that the vasoactive dipeptide Trp-His possesses inhibitory activity against Ca²⁺-CaM complex formation, which may elucidate how Trp-His inhibited CaMKII in a previous study.
  
  
  CONCLUSIONS
  The results provide a basic idea that could lead to the development of small peptides binding with high affinity to CaM and inhibiting Ca²⁺-CaM complex formation in the future.
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Thanutchaporn
authors.initials: T
authors.lastname: Kumrungsee
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Saiki
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Akiyama
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Nakashima
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
authors.forename: Yutaro
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan. Electronic address: tmatsui@agr.kyushu-u.ac.jp.
authors.forename: Toshiro
authors.initials: T
authors.lastname: Matsui
mesh_terms: D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D004151:Dipeptides / Q000737:chemistry* / Q000378:metabolism; D014665:Vasodilator Agents / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002147:Calmodulin; D004151:Dipeptides; D014665:Vasodilator Agents; D002118:Calcium
keywords: Ca(2+)-calmodulin complex; Dipeptide; MD simulation