The molecular appearance of native TRPM7 channel complexes identified by high-resolution proteomics

The transient receptor potential melastatin-subfamily member 7 (TRPM7) is a ubiquitously expressed membrane protein consisting of ion channel and protein kinase domains. TRPM7 plays a fundamental role in the cellular uptake of divalent cations such as Zn²⁺, Mg²⁺ and Ca²⁺, and thus shapes cellular excitability, plasticity and metabolic activity. The molecular appearance and operation of TRPM7 channel complexes in native tissues have remained unresolved. Here, we investigated the subunit composition of endogenous TRPM7 channels in rodent brain by multi-epitope affinity purification and high-resolution quantitative MS analysis. We found that native TRPM7 channels are high molecular-weight multi-protein complexes that contain the putative metal transporter proteins CNNM1-4 and a small G-protein ARL15. Heterologous reconstitution experiments confirmed the formation of TRPM7/CNNM/ARL15 ternary complexes and indicated that ARL15 effectively and specifically impacts TRPM7 channel activity. These results open up new avenues towards a mechanistic understanding of the cellular regulation and function of TRPM7 channels.