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Subunit composition of mammalian transient receptor potential channels in living cells
Thomas Hofmann1, Michael Schaefer, Günter Schultz
1Institut für Pharmakologie und Toxikologie, Philipps-Universität Marburg, Karl-von-Frisch-Strasse 1, D-35033 Marburg, Germany.
Abstract:
Hormones, neurotransmitters, and growth factors give rise to calcium entry via receptor-activated cation channels that are activated downstream of phospholipase C activity. Members of the transient receptor potential channel (TRPC) family have been characterized as molecular substrates mediating receptor-activated cation influx. TRPC channels are assumed to be composed of multiple TRPC proteins. However, the cellular principles governing the assembly of TRPC proteins into homo- or heteromeric ion channels still remain elusive. By pursuing four independent experimental approaches--i.e., subcellular cotrafficking of TRPC subunits, differential functional suppression by dominant-negative subunits, fluorescence resonance energy transfer between labeled TRPC subunits, and coimmunoprecipitation--we investigate the combinatorial rules of TRPC assembly. Our data show that (i) TRPC2 does not interact with any known TRPC protein and (ii) TRPC1 has the ability to form channel complexes together with TRPC4 and TRPC5. (iii) All other TRPCs exclusively assemble into homo- or heterotetramers within the confines of TRPC subfamilies--e.g., TRPC4/5 or TRPC3/6/7. The principles of TRPC channel formation offer the conceptual framework to assess the physiological role of distinct TRPC proteins in living cells.
Insights
Transient Receptor Potential channel (TRPC) assembly rules reveal specific subunit interactions. TRPC1 forms complexes with TRPC4/5, while others form homomers or heteromers within subfamilies.
Area of Science:
- Molecular biology
- Cell physiology
- Ion channel biophysics
Background:
- Receptor-activated calcium entry is crucial for cellular signaling, mediated by phospholipase C activity.
- Transient Receptor Potential channel (TRPC) proteins are key players in this calcium influx.
- The assembly principles of TRPC subunits into functional homo- or heteromeric channels are not well understood.
Purpose of the Study:
- To elucidate the combinatorial rules governing the assembly of TRPC proteins into ion channels.
- To determine which TRPC subunits can form functional channel complexes.
- To understand the structural basis of TRPC channel diversity.
Main Methods:
- Subcellular co-trafficking assays of TRPC subunits.
- Functional analysis using dominant-negative TRPC subunits.
- Förster resonance energy transfer (FRET) to study subunit proximity.
- Co-immunoprecipitation to confirm protein interactions.
Main Results:
- TRPC2 does not interact with any other known TRPC protein.
- TRPC1 can form channel complexes with TRPC4 and TRPC5.
- Other TRPC proteins exclusively form homomeric or heteromeric tetramers within their respective subfamilies (e.g., TRPC4/5, TRPC3/6/7).
Conclusions:
- Established combinatorial rules for TRPC subunit assembly.
- Demonstrated specific interaction patterns, including TRPC1 with TRPC4/5 and subfamily-specific assembly.
- Provides a framework for investigating the physiological roles of specific TRPC channels.