Abstract
Binding of IP3 (inositol 1,4,5-trisphosphate) to the IP3-binding core (residues 224–604) of IP3Rs (IP3 receptors) initiates opening of these ubiquitous intracellular Ca2+ channels. The mechanisms are unresolved, but require conformational changes to pass through the suppressor domain (residues 1–223). A calmodulin-binding peptide derived from myosin light chain kinase uncouples these events. We identified a similar conserved 1-8-14 calmodulin-binding motif within the suppressor domain of IP3R1 and, using peptides and mutagenesis, we demonstrate that it is essential for IP3R activation, whether assessed by IP3-evoked Ca2+ release or patch-clamp recoding of nuclear IP3R. Mimetic peptides specifically inhibit activation of IP3R by uncoupling the IP3-binding core from the suppressor domain. Mutations of key hydrophobic residues within the endogenous 1-8-14 motif mimic the peptides. Our results show that an endogenous 1-8-14 motif mediates conformational changes that are essential for IP3R activation. The inhibitory effects of calmodulin and related proteins may result from disruption of this essential interaction.
Highlights
Ca2+ channels allow most electrical and many chemical signals to be transduced into the changes in cytosolic Ca2+ concentration that regulate almost every aspect of cellular activity [1]
By analogy c The Authors Journal compilation c 2013 Biochemical Society with ryanodine receptor (RyR), that inhibition of IP3 receptor (IP3R) by myosin light chain kinase (MLCK) peptide might result from disruption of an interaction between endogenous CaM-like and CaM-binding domains within IP3Rs, and that, for IP3Rs, this interaction is essential for activation
A sequence within the suppressor domain (SD) of all known IP3Rs includes the critical hydrophobic residues of a 1-8-14 CaM-binding motif appropriately oriented within the known structure of the SD [41] (Figures 1B and 1C)
Summary
Ca2+ channels allow most electrical and many chemical signals to be transduced into the changes in cytosolic Ca2+ concentration that regulate almost every aspect of cellular activity [1]. By analogy c The Authors Journal compilation c 2013 Biochemical Society with RyRs, that inhibition of IP3Rs by MLCK peptide might result from disruption of an interaction between endogenous CaM-like and CaM-binding domains within IP3Rs, and that, for IP3Rs, this interaction is essential for activation.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
