Abstract
Transient receptor potential (TRPs) channels are crucial downstream targets of calcium signalling cascades. They can be modulated either by calcium itself and/or by calcium-binding proteins (CBPs). Intracellular messengers usually interact with binding domains present at the most variable TRP regions—N- and C-cytoplasmic termini. Calmodulin (CaM) is a calcium-dependent cytosolic protein serving as a modulator of most transmembrane receptors. Although CaM-binding domains are widespread within intracellular parts of TRPs, no such binding domain has been characterised at the TRP melastatin member—the transient receptor potential melastatin 6 (TRPM6) channel. Another CBP, the S100 calcium-binding protein A1 (S100A1), is also known for its modulatory activities towards receptors. S100A1 commonly shares a CaM-binding domain. Here, we present the first identified CaM and S100A1 binding sites at the N-terminal of TRPM6. We have confirmed the L520-R535 N-terminal TRPM6 domain as a shared binding site for CaM and S100A1 using biophysical and molecular modelling methods. A specific domain of basic amino acid residues (R526/R531/K532/R535) present at this TRPM6 domain has been identified as crucial to maintain non-covalent interactions with the ligands. Our data unambiguously confirm that CaM and S100A1 share the same binding domain at the TRPM6 N-terminus although the ligand-binding mechanism is different.
Highlights
Transient receptor potential melastatin (TRPM) channels are an eight-member subfamily of the cation-permeable transient receptor potential (TRP) superfamily, which exhibits heterogeneous functions and expression patterns [1]
The TRPs binding domains hydrophobic motifs participate in formations of first contacts with the hydrophobic patch of the CaM/ Ca2+ complex
TRPM6np involves a cluster of five basic residues: R523, R526, R531, K532, and R535
Summary
Transient receptor potential melastatin (TRPM) channels are an eight-member subfamily of the cation-permeable transient receptor potential (TRP) superfamily, which exhibits heterogeneous functions and expression patterns [1]. The TRPM6 channel acts as a voltage-independent divalent cation channel with a 5-fold higher permeability for Mg2+ than for Ca2+ [2] This channel is a tissue-specific receptor predominantly expressed in the intestinal and renal epithelium, where it provides absorption and reabsorption of Mg2+ [2,3,4]. TRP cytoplasmic tails substantially differ between members and contain multiple binding motifs and domains [21,22] affecting channel function [23]. TRP modulation is affected by many intracellular and extracellular binding agents; they commonly stimulate the activity of the channel or inhibit it [24]. TRPM6 activity is suppressed by free intracellular Mg2+ [14,34,35]; channel regulation by Ca2+ has not been proved [34,35,36]
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
