Nanoscale organization of the MEC-4 DEG/ENaC sensory mechanotransduction channel in Caenorhabditis elegans touch receptor neurons.
Hearing, touch and proprioception are thought to involve direct activation of mechano-electrical transduction (MeT) channels. In Caenorhabditis elegans touch receptor neurons (TRNs), such channels contain two pore-forming subunits (MEC-4 and MEC-10) and two auxiliary subunits (MEC-2 and MEC-6). MEC-4 and MEC-10 belong to a large superfamily of ion channel proteins (DEG/ENaCs) that form nonvoltage-gated, amiloride-sensitive Na+ channels. In TRNs, unique 15-protofilament microtubules and an electron-dense extracellular matrix have been proposed to serve as gating tethers critical for MeT channel activation. We combined high-pressure freezing and serial-section immunoelectron microscopy to determine the position of MeT channels relative to putative gating tethers. MeT channels were visualized using antibodies against MEC-4 and MEC-2. This nanometer-resolution view of a sensory MeT channel establishes structural constraints on the mechanics of channel gating. We show here that MEC-2 and MEC-5 collagen, a putative extracellular tether, occupy overlapping but distinct domains in TRN neurites. Although channels decorate all sides of TRN neurites; they are not associated with the distal endpoints of 15-protofilament microtubules hypothesized to be gating tethers. These specialized microtubules, which are unique to TRNs, assemble into a cross-linked bundle connected by a network of kinked filaments to the neurite membrane. We speculate that the microtubule bundle converts external point loads into membrane stretch which, in turn, facilitates MeT channel activation.
Cueva
Juan G
JG
Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA.
Mulholland
Atticus
A
Goodman
Miriam B
MB
D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins / Q000032:analysis / Q000378:metabolism / Q000648:ultrastructure*; D053503:Epithelial Sodium Channels / Q000032:analysis / Q000378:metabolism / Q000648:ultrastructure*; D008465:Mechanoreceptors / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D009474:Neurons / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D011984:Sensory Receptor Cells / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D015222:Sodium Channels / Q000032:analysis / Q000378:metabolism / Q000648:ultrastructure*; D014110:Touch / Q000502:physiology
D029742:Caenorhabditis elegans Proteins; C094927:Deg-1 protein, C elegans; D053503:Epithelial Sodium Channels; C115871:Mec-4 protein, C elegans; D008565:Membrane Proteins; D015222:Sodium Channels