The nhTMEM16 Scramblase Is Also a Nonselective Ion Channel
Related Experiment Video
Updated: Mar 12, 2026
A Fluorescence-based Assay of Phospholipid Scramblase Activity
Published on: September 20, 2016
Byoung-Cheol Lee1, Anant K Menon2, Alessio Accardi3
1Department of Anesthesiology, Weill Cornell Medical College, New York, New York.
Abstract:
The TMEM16 family comprises Ca2+-activated Cl- channels and phospholipid scramblases. The crystal structure of a fungal homolog, nhTMEM16, revealed an important architectural feature of this protein family in the form of a bilayer-spanning hydrophilic groove that is directly exposed to the membrane. This groove likely provides a pathway for lipid translocation. As mutations that alter ion channel activity of the TMEM16 proteins localize around the groove, it was suggested that the ion and lipid pathways coincide such that the ion pore is partly lined by phospholipids. However, this proposal was not supported by the observation that nhTMEM16 does not mediate ion transport. Here we show that nhTMEM16 mediates both ion and lipid transport and that its properties closely resemble those of a previously characterized fungal homolog, afTMEM16. We show that the reported lack of ion transport activity of nhTMEM16 is due to the lipid composition of the reconstitution membranes and to the presence of a GFP tag. Thus, nhTMEM16, like afTMEM16 and the mammalian TMEM16F, mediates simultaneous lipid scrambling and nonspecific ion transport. This supports the hypothesis that these two processes are tightly correlated and likely to be a general functional feature of the TMEM16 scramblases and therefore of general importance in understanding their biological roles.
Insights
The TMEM16 family of proteins, including nhTMEM16, are shown to transport both ions and lipids. This finding supports the idea that lipid scrambling and ion transport are linked functions within these important biological molecules.
Area of Science:
- Biochemistry
- Molecular Biology
- Membrane Protein Function
Background:
- The TMEM16 family proteins are known as calcium-activated chloride channels and phospholipid scramblases.
- The crystal structure of fungal nhTMEM16 revealed a membrane-exposed hydrophilic groove, suggesting a lipid translocation pathway.
- Previous studies proposed coinciding ion and lipid pathways, but nhTMEM16 was thought to lack ion transport activity.
Purpose of the Study:
- To investigate the dual ion and lipid transport capabilities of the fungal TMEM16 homolog, nhTMEM16.
- To clarify the functional relationship between lipid scrambling and ion transport in the TMEM16 protein family.
- To re-evaluate the proposed model of ion and lipid pathways within TMEM16 proteins.
Main Methods:
- Reconstitution of purified nhTMEM16 into liposomes with varying lipid compositions.
- Functional assays to measure both lipid scrambling and ion transport activities.
- Comparison of nhTMEM16 properties with other TMEM16 family members, including afTMEM16 and TMEM16F.
Main Results:
- nhTMEM16 demonstrates significant ion transport activity, contrary to previous reports.
- The apparent lack of ion transport was attributed to specific membrane lipid compositions and the presence of a GFP tag.
- nhTMEM16 mediates simultaneous lipid scrambling and non-specific ion transport, similar to afTMEM16 and TMEM16F.
Conclusions:
- The TMEM16 protein family, including fungal homologs, possesses dual ion and lipid transport functions.
- Ion and lipid transport are tightly correlated and likely a general feature of TMEM16 scramblases.
- This dual function is crucial for understanding the broader biological roles of TMEM16 proteins.
More Related Videos
08:55Single-Molecule Imaging of Lateral Mobility and Ion Channel Activity in Lipid Bilayers using Total Internal Reflection Fluorescence TIRF Microscopy
Published on: February 17, 2023
07:47A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters
Published on: April 20, 2015
Related Concept Videos
01:19Membrane Asymmetry Regulating Transporters
Flippase
Eukaryotic flippases are type-IV P-type ATPases or P4-ATPases belonging to P-type ATPase family proteins that are membrane-bound pumps involved in the ATP-mediated transport of ions and molecules across the membrane. Flippases flip specific phospholipids from the outer to the inner leaflet of a membrane. All P4-ATPases have one...
01:24Non-gated Ion Channels
Compared to the gated ion channels, the non-gated channels, also known as leakage or passive channels, have no gating mechanism....
01:24Non-gated Ion Channels
01:12Mechanically-gated Ion Channels
01:12Mechanically-gated Ion Channels
01:28Assembly of the Lipid Bilayer in the ER
A large chunk of any biological membrane is composed of phospholipids. These lipids have a heterogeneous distribution across different subcellular organelles and even between...