A transmembrane domain of the putative channel subunit MEC-4 influences mechanotransduction and neurodegeneration in C. elegans.
Aberrant ion channel activity plays a causative role in several human disorders. Inappropriately regulated channel activity also appears to be the basis for neurodegeneration induced by dominant mutations of Caenorhabditis elegans mec-4 (mec-4(d)), a member of the degenerin gene family postulated to encode a subunit of a mechanosensory channel. The degenerin gene family has been defined by two C. elegans genes, mec-4 and deg-1, which can mutate to gain-of-function alleles that induce degeneration of specific groups of neurons. A related mammalian gene, rat alpha-rENaC, induces an amiloride-sensitive Na+ current when introduced to Xenopus oocytes, strongly suggesting that degenerin genes encode ion channel proteins. Deduced amino-acid sequences of the degenerins include two predicted membrane-spanning domains. Here we show that conserved amino acids within the second membrane-spanning domain (MSDII) are critical for MEC-4 activity and that specific substitutions within MSDII, whether encoded in cis or in trans to a mec-4(d) mutation, block or delay the onset of degeneration. Remarkably, MSDII from two other family members, C. elegans deg-1 and rat alpha-rENaC, can functionally substitute for MEC-4 MSDII in chimaeric proteins. Our results support a structural model for a mechanosensory channels in which multiple MEC-4 subunits are oriented such that MSDII lines the channel pore, and a neurodegeneration model in which aberrant ion flow through this channel is a key event.
Hong
K
K
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08855.
Driscoll
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D000483:Alleles; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins; D017124:Conserved Sequence; D017931:DNA Primers; D015801:Helminth Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008465:Mechanoreceptors / Q000737:chemistry* / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009410:Nerve Degeneration / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology*; D051381:Rats
D000596:Amino Acids; D029742:Caenorhabditis elegans Proteins; D017931:DNA Primers; D015801:Helminth Proteins; C115871:Mec-4 protein, C elegans; D008565:Membrane Proteins