Études de type structure fonction des mutations causant l’ataxie épisodique de type I sur les canaux potassiques dépendants du voltage
The genetic episodic ataxias form a group of disorders with heterogeneous phenotype and genotype, but share the common feature of intermittent cerebellar dysfunction. Episodic ataxia (EA) types 1 and 2 are most widely recognised amongst the autosomal dominant episodic ataxias and are caused by dysfunction of neuronal voltage-gated ion channels. The present study focuses on mutations causing EA-1 located in the voltage sensor domains (VSDs) of Kv1.1. A member of the Shaker channel family. Here, we have characterised the electrophysiological properties of six different mutations at the position of F244 and we also reported the partiality effects of these following mutations T284A/M, R297K/Q/A/H, I320T, L375F, L399I S412C/I on Shaker sequence using the cut open voltage clamp technique (COVC). We have shown that mutations of F244 in the S1 of the Shaker Kv channel positively shift the voltage dependence of the VSD movement and alter functional coupling between VSD and pore domain. The mutations causing immobilization of the VSD movement during activation and deactivation and responsible for creating a leak current during activation, are removed by the application of 4-AP (4-aminopyridine) or by reinsertion of N-type inactivation but not by TEA (tetraethylamonium). Insights into the molecular mechanisms responsible for the stabilization of the intermediate state have been investigated by separately neutralizing the first three charges (R1Q, R2Q and R3Q) in the S4 segment. The result suggests an interaction between R2 and F244 mutants. It was established that a second co-evolved interface exists between S1 and the pore helix near the extracellular surface and it acts as a second anchor point. It is also responsible for generation of leak currents. The results suggest a dysfunction of the VSD in which the affected nerve cells cannot efficiently repolarize following an action potential because of altered delayed rectifier function
Voltage-gated potassium channel Gating Intermediate state trapping Voltage sensor domains Leak current