Targeting of voltage-gated calcium channel α2δ-1 subunit to lipid rafts is independent from a GPI-anchoring motif

PLoS One. 2011;6(6):e19802. doi: 10.1371/journal.pone.0019802. Epub 2011 Jun 10.

Abstract

Voltage-gated calcium channels (Ca(v)) exist as heteromultimers comprising a pore-forming α(1) with accessory β and α(2)δ subunits which modify channel trafficking and function. We previously showed that α(2)δ-1 (and likely the other mammalian α(2)δ isoforms--α(2)δ-2, 3 and 4) is required for targeting Ca(v)s to lipid rafts, although the mechanism remains unclear. Whilst originally understood to have a classical type I transmembrane (TM) topology, recent evidence suggests the α(2)δ subunit contains a glycosylphosphatidylinositol (GPI)-anchor that mediates its association with lipid rafts. To test this notion, we have used a strategy based on the expression of chimera, where the reported GPI-anchoring sequences in the gabapentinoid-sensitive α(2)δ-1 subunit have been substituted with those of a functionally inert Type I TM-spanning protein--PIN-G. Using imaging, electrophysiology and biochemistry, we find that lipid raft association of PIN-α(2)δ is unaffected by substitution of the GPI motif with the TM domain of PIN-G. Moreover, the presence of the GPI motif alone is not sufficient for raft localisation, suggesting that upstream residues are required. GPI-anchoring is susceptible to phosphatidylinositol-phospholipase C (PI-PLC) cleavage. However, whilst raft localisation of PIN-α(2)δ is disrupted by PI-PLC treatment, this is assay-dependent and non-specific effects of PI-PLC are observed on the distribution of the endogenous raft marker, caveolin, but not flotillin. Taken together, these data are most consistent with a model where α(2)δ-1 retains its type I transmembrane topology and its targeting to lipid rafts is governed by sequences upstream of the putative GPI anchor, that promote protein-protein, rather than lipid-lipid interactions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Animals
  • Biophysical Phenomena
  • Calcium Channels / chemistry*
  • Calcium Channels / metabolism*
  • Calcium Channels, L-Type
  • Caveolins / metabolism
  • Glycosylphosphatidylinositols / metabolism*
  • Membrane Microdomains / metabolism*
  • Membrane Proteins / metabolism
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • Phosphoinositide Phospholipase C / metabolism
  • Protein Subunits / metabolism*
  • Protein Transport
  • Rabbits
  • Rats
  • Recombinant Fusion Proteins / metabolism
  • Sucrose / metabolism

Substances

  • Cacna2d1 protein, rat
  • Calcium Channels
  • Calcium Channels, L-Type
  • Caveolins
  • Glycosylphosphatidylinositols
  • Membrane Proteins
  • Mutant Proteins
  • Protein Subunits
  • Recombinant Fusion Proteins
  • flotillins
  • Sucrose
  • Phosphoinositide Phospholipase C