Acidic residues on the voltage sensor domain determine the activation of the NaChBac sodium channel

¹ Laval University

^* To whom correspondence should be addressed. E-mail: mohamed.chahine{at}phc.ulaval.ca.

Submitted on June 3, 2006
Revised on July 13, 2006
Accepted on 27 December 2006

	Abstract

The voltage-sensing domain of voltage-gated ion channels is characterized by specific, conserved, charged residues. Positively charged residues on segment S4 are the main contributors to voltage sensing and negatively charged residues on the S2 and S3 segments are believed to participate to the process. However, their function in the voltage sensor is not well understood. To probe the role of three acidic residues in NaChBac (D58 and E68 in S2, and D91 in S3), we employed site-directed mutagenesis to substitute native acidic residues with cysteine (neutral), lysine (positive charge) or either aspartate or glutamate (negative charge). We used a combination of the patch clamp technique to record Na+ currents and molecular modeling to visualize interacting amino acid residues. We suggest that the acidic residues on the S2 and S3 segments form specific interactions with adjacent amino acids in the voltage sensor domain. The main interactions in NaChBac are D58 (S2) with A97-G98 (S3) and R120 (S4), E68 (S2) with R129 (L4-5) and D91 (S3) with R72 (S2). Changing these acidic residues modified the interactions, which in turn altered the sensitivity of the voltage sensor.

Key Words: Bacillus haloduran, S4 segment, gating charges, molecular modeling, patch clamp, voltage-gated Na+ channel