New Hyperekplexia Mutations Provide Insight into Glycine Receptor Assembly, Trafficking, and Activation Mechanisms

Abstract

Background: Hyperekplexia mutations have provided much information about glycine receptor structure and function. Results: We identified and characterized nine new mutations. Dominant mutations resulted in spontaneous activation, whereas recessive mutations precluded surface expression. Conclusion: These data provide insight into glycine receptor activation mechanisms and surface expression determinants. Significance: The results enhance our understanding of hyperekplexia pathology and glycine receptor structure-function.

Correlating Structural and Energetic Changes in Glycine Receptor Activation

“…We also observed spontaneous channel activity in ␣1 QϪ26ЈE homomeric receptors ( Fig. 2B above), as previously reported (13). As evidence was adduced for an interaction between the introduced glutamic acid at Ϫ26Ј in one subunit and the Arg 19 Ј position in the adjacent subunit (22) we investigated the effect of introducing the wild-type ␤ subunit, which has an alanine at 19Ј.…”

“…Similarly, the ␣1 K24ЈE mutation reduces glycine sensitivity in both homo-and heteromeric GlyRs, although no change in single channel conductance was reported (5,11,12). A recently identified third mutation, ␣1 Q226E (␣1 QϪ26ЈE ), located near the top of M1, gives rise to spontaneous channel opening, a reduction in single channel conductance, but no significant change in whole cell agonist sensitivity (13).of residues at 19Ј, 24Ј, and Ϫ26Ј. A high degree of sequence conservation is also evident at these positions, especially among anion-selective pLGICs, suggesting a common functional relevance.…”

Allosteric and hyperekplexic mutant phenotypes investigated on an α 1 glycine receptor transmembrane structure

“…On the α 1 GlyR, the Q226E and R271Q mutations do not reveal coupling energy between the two positions, but a series of other mutations support the above conclusion (22). Data were previously interpreted on the basis of a speculative gating model between ELIC (closed) and GLIC (open) (22,23), where M2 and M3 tilt altogether as a rigid block. Here we provide a different gating model supported by a combination of electrophysiological, X-ray, and modeling data that mainly involve motion of M2 alone (Fig.…”

“…Recently, Q226E was reported to produce spontaneously open channels (22,23). On Lily, this mutation equally produces constitutive opening: (i) Immediately after the whole-cell clamping at pH 8.0, cells expressing Q226E generate high-leak currents (∼600 pA) that are blocked by 100 μM of picrotoxin; application of a more acidic solution further increases the currents, but the bad shape of the cells precluded repetitive stimulations and measurement of dose-response curves; and (ii) single-channel recording at pH 8.0 shows repetitive spontaneous openings (Fig.…”

Glycine is able to induce both a motility speed in- and decrease during zebrafish neuronal migration

“…We aimed to increase the speed reduction effect by overexpressing gain-of-function mutations in glycine receptors. The mutations are modelled on available human patient data, and correspond to zebrafish GlyRa1 I67F [18,19], GlyRa1 V304M [18,20,21], and rat GlyRa3 P185L [22]. In contrast to expectations, all of these mutations led to a moderate THN speed increase in phase 2 (approx.…”