A calmodulin antagonist reveals a calmodulin-independent interdomain interaction essential for activation of inositol 1,4, 5-trisphosphate receptors

作者：Sun Yi; Taylor Colin W^*

来源：Biochemical Journal, 2008, 416: 243-253.

DOI：10.1042/BJ20080861

• Ca(2+) channel
• Ca(2+) signalling
• calmodulin
• inositol 1,4,5-trisphosphate receptor (IP(3)R)
• myosin light chain kinase

CaM (calmodulin) has been implicated in the regulation Of IP(3)R [IP(3) (inositol 1,4,5-trisphosphate) receptors] and a recent report suggested that CaM tightly tethered to IP3R wits essential for IP3R activation [Nadif Kasri, Torok, Galione, Garnham, Callewaert, Missiaen, Parys and De Smedt (2006) J. Biol. Chem. 281, 83328338]. In the present study, we confirm that a CaM-binding peptide derived from MLCK (myosin light chain kinase) inhibits IP(3)-evoked C,121 release via all three IP(3)R subtypes. However, inhibition by MLCK peptide is not mimicked by other CaM antagonists that effectively block regulation Of IP3R by CaM. Inhibition by MLCK peptide is rapid, fully reversible and occurs under conditions where there is no CaM associated With IP(3)R. MLCK peptide stimulates IP(3) binding to IP3R I and to its bacterially expressed N-terminal, but not after removal of the suppressor domain (residues 1-224). We suggest that MLCK peptide mimics a sequence within the suppressor domain that is similar to a 1-8-14 CaM-binding motif. The peptide may thereby unzip an interdomain interaction that is essential for IP3R activation. We conclude that CaM is not essential for IP3R activation, and that MLCK peptide is a selective antagonist of the IP3R that binds directly to the N-terminal to uncouple IP3 binding from channel gating. The results of the present study highlight the importance of the suppressor domain in IP3R activation and suggest that MLCK peptide may provide a route to novel non-competitive antagonists of MR.

• 出版日期2008-12-1