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The DEG/ENaC protein MEC-10 regulates the transduction channel complex in Caenorhabditis elegans touch receptor neurons.

ABSTRACT: Gentle touch sensation in Caenorhabditis elegans is mediated by the MEC-4/MEC-10 channel complex, which is expressed exclusively in six touch receptor neurons (TRNs). The complex contains two pore-forming subunits, MEC-4 and MEC-10, as well as the accessory subunits MEC-2, MEC-6, and UNC-24. MEC-4 is essential for channel function, but beyond its role as a pore-forming subunit, the functional contribution of MEC-10 to the channel complex and to touch sensation is unclear. We addressed this question using behavioral assays, in vivo electrophysiological recordings from TRNs, and heterologous expression of mutant MEC-10 isoforms. Animals with a deletion in mec-10 showed only a partial loss of touch sensitivity and a modest decrease in the size of the mechanoreceptor current (MRC). In contrast, five previously identified mec-10 alleles acted as recessive gain-of-function alleles that resulted in complete touch insensitivity. Each of these alleles produced a substantial decrease in MRC size and a shift in the reversal potential in vivo. The latter finding indicates that these mec-10 mutations alter the ionic selectivity of the transduction channel in vivo. All mec-10 mutant animals had properly localized channel complexes, indicating that the loss of MRCs was not attributable to a dramatic mislocalization of transduction channels. Finally, electrophysiological examination of heterologously expressed complexes suggests that mutant MEC-10 proteins may affect channel current via MEC-2.

SUBMITTER: Arnadottir J

PROVIDER: S-EPMC3172708 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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The DEG/ENaC protein MEC-10 regulates the transduction channel complex in Caenorhabditis elegans touch receptor neurons.

Arnadóttir Jóhanna J O'Hagan Robert R Chen Yushu Y Goodman Miriam B MB Chalfie Martin M

The Journal of neuroscience : the official journal of the Society for Neuroscience 20110801 35

Gentle touch sensation in Caenorhabditis elegans is mediated by the MEC-4/MEC-10 channel complex, which is expressed exclusively in six touch receptor neurons (TRNs). The complex contains two pore-forming subunits, MEC-4 and MEC-10, as well as the accessory subunits MEC-2, MEC-6, and UNC-24. MEC-4 is essential for channel function, but beyond its role as a pore-forming subunit, the functional contribution of MEC-10 to the channel complex and to touch sensation is unclear. We addressed this quest ...[more]

PMID: 21880930

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Project description:MEC-4 and MEC-10 are the pore-forming subunits of the sensory mechanotransduction complex that mediates touch sensation in Caenorhabditis elegans (O'Hagan, R., M. Chalfie, and M.B. Goodman. 2005. Nat. Neurosci. 8:43-50). They are members of a large family of ion channel proteins, collectively termed DEG/ENaCs, which are expressed in epithelial cells and neurons. In Xenopus oocytes, MEC-4 can assemble into homomeric channels and coassemble with MEC-10 into heteromeric channels (Goodman, M.B., G.G. Ernstrom, D.S. Chelur, R. O'Hagan, C.A. Yao, and M. Chalfie. 2002. Nature. 415:1039-1042). To gain insight into the structure-function principles that govern gating and drug block, we analyzed the effect of gain-of-function mutations using a combination of two-electrode voltage clamp, single-channel recording, and outside-out macropatches. We found that mutation of A713, the d or degeneration position, to residues larger than cysteine increased macroscopic current, open probability, and open times in homomeric channels, suggesting that bulky residues at this position stabilize open states. Wild-type MEC-10 partially suppressed the effect of such mutations on macroscopic current, suggesting that subunit-subunit interactions regulate open probability. Additional support for this idea is derived from an analysis of macroscopic currents carried by single-mutant and double-mutant heteromeric channels. We also examined blockade by the diuretic amiloride and two related compounds. We found that mutation of A713 to threonine, glycine, or aspartate decreased the affinity of homomeric channels for amiloride. Unlike the increase in open probability, this effect was not related to size of the amino acid side chain, indicating that mutation at this site alters antagonist binding by an independent mechanism. Finally, we present evidence that amiloride block is diffusion limited in DEG/ENaC channels, suggesting that variations in amiloride affinity result from variations in binding energy as opposed to accessibility. We conclude that the d position is part of a key region in the channel functionally and structurally, possibly representing the beginning of a pore-forming domain.

Dataset Information

The DEG/ENaC protein MEC-10 regulates the transduction channel complex in Caenorhabditis elegans touch receptor neurons.

Publications

The DEG/ENaC protein MEC-10 regulates the transduction channel complex in Caenorhabditis elegans touch receptor neurons.

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