Browsing by Author "Stringer, Robin N"

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    A rare CACNA1H variant associated with amyotrophic lateral sclerosis causes complete loss of Cav3.2 T-type channel activity
    (2020-03-06) Stringer, Robin N; Jurkovicova-Tarabova, Bohumila; Huang, Sun; Haji-Ghassemi, Omid; Idoux, Romane; Liashenko, Anna; Souza, Ivana A; Rzhepetskyy, Yuriy; Lacinova, Lubica; Van Petegem, Filip; Zamponi, Gerald W; Pamphlett, Roger; Weiss, Norbert
    Abstract Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by the progressive loss of cortical, brain stem and spinal motor neurons that leads to muscle weakness and death. A previous study implicated CACNA1H encoding for Cav3.2 calcium channels as a susceptibility gene in ALS. In the present study, two heterozygous CACNA1H variants were identified by whole genome sequencing in a small cohort of ALS patients. These variants were functionally characterized using patch clamp electrophysiology, biochemistry assays, and molecular modeling. A previously unreported c.454GTAC > G variant produced an inframe deletion of a highly conserved isoleucine residue in Cav3.2 (p.ΔI153) and caused a complete loss-of-function of the channel, with an additional dominant-negative effect on the wild-type channel when expressed in trans. In contrast, the c.3629C > T variant caused a missense substitution of a proline with a leucine (p.P1210L) and produced a comparatively mild alteration of Cav3.2 channel activity. The newly identified ΔI153 variant is the first to be reported to cause a complete loss of Cav3.2 channel function. These findings add to the notion that loss-of-function of Cav3.2 channels associated with rare CACNA1H variants may be risk factors in the complex etiology of ALS.
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    Functional identification of potential non-canonical N-glycosylation sites within Cav3.2 T-type calcium channels
    (2020-11-11) Ficelova, Vendula; Souza, Ivana A; Cmarko, Leos; Gandini, Maria A; Stringer, Robin N; Zamponi, Gerald W; Weiss, Norbert
    Abstract Low-voltage-activated T-type calcium channels are important contributors to nervous system function. Post-translational modification of these channels has emerged as an important mechanism to control channel activity. Previous studies have documented the importance of asparagine (N)-linked glycosylation and identified several asparagine residues within the canonical consensus sequence N-X-S/T that is essential for the expression and function of Cav3.2 channels. Here, we explored the functional role of non-canonical N-glycosylation motifs in the conformation N-X-C based on site directed mutagenesis. Using a combination of electrophysiological recordings and surface biotinylation assays, we show that asparagines N345 and N1780 located in the motifs NVC and NPC, respectively, are essential for the expression of the human Cav3.2 channel in the plasma membrane. Therefore, these newly identified asparagine residues within non-canonical motifs add to those previously reported in canonical sites and suggest that N-glycosylation of Cav3.2 may also occur at non-canonical motifs to control expression of the channel in the plasma membrane. It is also the first study to report the functional importance of non-canonical N-glycosylation motifs in an ion channel.