Ankyrin G restricts ion channel diffusion at the axonal initial segment before the establishment of the diffusion barrier.
In mammalian neurons, the precise accumulation of sodium channels at the axonal initial segment (AIS) ensures action potential initiation. This accumulation precedes the immobilization of membrane proteins and lipids by a diffusion barrier at the AIS. Using single-particle tracking, we measured the mobility of a chimeric ion channel bearing the ankyrin-binding motif of the Nav1.2 sodium channel. We found that ankyrin G (ankG) limits membrane diffusion of ion channels when coexpressed in neuroblastoma cells. Site-directed mutants with decreased affinity for ankG exhibit increased diffusion speeds. In immature hippocampal neurons, we demonstrated that ion channel immobilization by ankG is regulated by protein kinase CK2 and occurs as soon as ankG accumulates at the AIS of elongating axons. Once the diffusion barrier is formed, ankG is still required to stabilize ion channels. In conclusion, our findings indicate that specific binding to ankG constitutes the initial step for Nav channel immobilization at the AIS membrane and precedes the establishment of the diffusion barrier.
Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Rercherche 641, Marseille F-13916, France.
Anna
A
Brachet
Christophe
C
Leterrier
Marie
M
Irondelle
Marie-Pierre
MP
Fache
Victor
V
Racine
Jean-Baptiste
JB
Sibarita
Daniel
D
Choquet
Bénédicte
B
Dargent
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017487:Ankyrins / Q000502:physiology*; D001369:Axons / Q000378:metabolism*; D001665:Binding Sites; D047390:Casein Kinase II / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D021381:Protein Transport; D016415:Sequence Alignment; D015222:Sodium Channels / Q000737:chemistry / Q000378:metabolism*
C094681:Ank3 protein, mouse; D017487:Ankyrins; D015222:Sodium Channels; D047390:Casein Kinase II