Emerging Concepts in Ion Channel Biophysics

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Emerging Concepts in Ion Channel Biophysics Poster Abstracts
58
58-POS Board 58
New Molecular Determinants of the Voltage-gated Na+ Channel Α/Β1 Functional Interface
Bertin Paiz-Candia1 , Thomas Scior1 , Angel Islas2,1, Alfredo Sánchez-Solano2, Claudia
Mancilla-Simbro2, Lourdes Millan-PerezPeña3, Eduardo M. Salinas-Stefanon2.
1Facultad de Ciencias Químicas, Universidad Autónoma de Puebla, Puebla, Puebla, Mexico,
2Laboratorio de Biofísica Instituto de Fisiología, Universidad Autónoma de Puebla, Puebla,
Mexico, 33Centro de Química, Instituto de Ciencias, Universidad Autónoma de Puebla, Puebla,
México, Puebla, Mexico.
Most of the inward Na+ currents responsible for the initiation of the action potential in vertebrate
excitable cells are modulated by membrane immunoglobulin-like (Ig-like) proteins called β1
auxiliary Na+ channel subunits. By the beginning of this century, chimeric studies on the β1-
induced electrophysiological modulation of Na+ channels had established that it is mediated by
an extracellular protein-protein interaction between the pore-forming α subunit and the Ig-like
domain of β1. Subsequently, our group has been amidst those who investigate such phenomena
at an atomistic level by computational means, i.e. via standard homology molecular modelling
and by a novel “analogy approach”. In the absence of the crystal structure of the β1 subunit, we
predicted two intramolecular bonds involved in the modulation of the rNav1.4 channel, a
disulphide and salt bridge, that were soon later observed in the crystal structure of β3 (a
homologue of β1, with a 44% sequence identity). We have also demonstrated that β1
significantly accelerates the inactivation of rNav1.4 channels, in which the intracellular
inactivation particle is absent, albeit within seconds. Exhaustive, unbiased sampling and
extremely low homology, “analogy modelling”, allowed the identification of two consecutive,
key residues on β1, whereby the double mutant: T109A N110A, we called TANA, caused a
pervasive electrophysiological loss-of-function. Mutant β1-TANA co-expression with rNav1.4:
i) abolished the β1-induced left-hand shift of the steady-state inactivation curve, ii) significantly
reduced the β1-induced acceleration of the inactivation and recovery from inactivation, and iii)
induced a current rundown upon repetitive depolarizations at 1, 2 and 5 Hz. These results may
delineate the functional mammalian Na+ channel α/β1 interface and may pave the way for
structure-based drug design targeting the β1 subunit, which incidentally also modulates the
response to some Na+ channel blockers.