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N-linked protein glycosylation is a major determinant for basal TRPC3 and TRPC6 channel activity
Alexander Dietrich1, Michael Mederos y Schnitzler, Jens Emmel
1Institut für Pharmakologie und Toxikologie, Philipps-Universität-Marburg, 35033 Marburg, Germany.
Abstract:
The TRPC family of receptor-activated cation channels (TRPC channels) can be subdivided into four subfamilies based on sequence homology as well as functional similarities. Members of the TRPC3/6/7 subfamily share common biophysical characteristics and are activated by diacylglycerol in a membrane-delimited manner. At present, it is only poorly understood whether members of the TRPC3/6/7 subfamily are functionally redundant or whether they serve distinct cellular roles. By electrophysiological and fluorescence imaging strategies we show that TRPC3 displays considerable constitutive activity, while TRPC6 is a tightly regulated channel. To identify potential molecular correlates accounting for the functional difference, we analyzed the glycosylation pattern of TRPC6 compared with TRPC3. Two NX(S/T) motifs in TRPC6 were mutated (Asn to Gln) by in vitro mutagenesis to delete one or both extracellular N-linked glycosylation sites. Immunoblotting analysis of HEK 293 cell lysates expressing TRPC6 wild type and mutants favors a model of TRPC6 that is dually glycosylated within the first (e1) and second extracellular loop (e2) as opposed to the monoglycosylated TRPC3 channel (Vannier, B., Zhu, X., Brown, D., and Birnbaumer, L. (1998) J. Biol. Chem. 273, 8675-8679). Elimination of the e2 glycosylation site, missing in the monoglycosylated TRPC3, was sufficient to convert the tightly receptor-regulated TRPC6 into a constitutively active channel, displaying functional characteristics of TRPC3. Reciprocally, engineering of an additional second glycosylated site in TRPC3 to mimic the glycosylation status in TRPC6 markedly reduced TRPC3 basal activity. We conclude that the glycosylation pattern plays a pivotal role for the tight regulation of TRPC6 through phospholipase C-activating receptors.
Insights
Glycosylation patterns differentiate TRPC3 and TRPC6 channels. Modifying TRPC6 glycosylation to mimic TRPC3 creates a constitutively active channel, revealing glycosylation
Area of Science:
- Molecular biology
- Cell physiology
- Ion channel research
Background:
- The TRPC channel family, particularly the TRPC3/6/7 subfamily, shares activation mechanisms but may have distinct cellular roles.
- Understanding functional differences between TRPC3 and TRPC6 is crucial for elucidating their specific physiological functions.
Purpose of the Study:
- To investigate the molecular basis for the functional divergence between TRPC3 and TRPC6 channels.
- To determine the role of glycosylation patterns in regulating TRPC6 channel activity.
Main Methods:
- Electrophysiology and fluorescence imaging to assess channel activity.
- In vitro mutagenesis to alter N-linked glycosylation sites in TRPC6.
- Immunoblotting to analyze glycosylation patterns in HEK 293 cells expressing TRPC wild-type and mutant channels.
Main Results:
- TRPC3 exhibits significant constitutive activity, whereas TRPC6 is tightly regulated by receptors.
- TRPC6 is dually glycosylated in extracellular loops (e1, e2), while TRPC3 is monoglycosylated.
- Eliminating the e2 glycosylation site in TRPC6 converted it to a constitutively active channel, mimicking TRPC3.
- Adding a second glycosylation site to TRPC3 reduced its basal activity, similar to TRPC6.
Conclusions:
- Glycosylation pattern is a key determinant of TRPC6 channel regulation.
- The presence or absence of specific N-linked glycosylation sites dictates the difference in basal and receptor-regulated activity between TRPC3 and TRPC6.
- This finding highlights the importance of post-translational modifications in ion channel function.