CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
The zinc binding site of the Shaker channel KDC1 from
Daucus carota
Cristiana Picco 1*, Alessia Naso 1, Paolo Soliani 1 and Franco Gambale 1
1 Istituto di Biofisica, Consiglio Nazionale delle Ricerche
* To whom correspondence should be addressed. E-mail: picco{at}ge.ibf.cnr.it.
Submitted on June 1, 2007
Revised on June 28, 2007
Accepted on 3 August 2007
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Abstract |
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KDC1 is a voltage-dependent Shaker-like potassium channel subunit cloned from Daucus carota which produces conductive channels in Xenopus oocytes only when co-expressed with other plant Shaker potassium subunits, such as KAT1 from Arabidopsis thaliana. External Zn2+ determines a potentiation of the current mediated by the dimeric construct KDC1-KAT1, which has been ascribed to zinc binding at a site comprising 3 histidines located at the S3-S4 (H161, H162) and S5-S6 (H224) linkers of KDC1. Here we demonstrate that also glutamate 164, located in close proximity of the KDC1 S4 segment, is an essential component of the zinc-binding site. On the contrary, glutamate 159, located in symmetrical position with respect to E164 in the sequence E159XHHXE164 but more distant from the voltage sensor, does not play any role in zinc binding. The effects of Zn2+ can be expressed as a "shift" of the gating parameters along the voltage axis. Kinetic modelling shows that Zn2+ slows the closing kinetics of KDC1-KAT1 without affecting the opening kinetics. Possibly, zinc affects the movement of the voltage sensor in and out of the membrane phase through electrostatic modification of a site close to the voltage sensor.
Key Words:
gating, metal, plant, potassium channel, voltage sensor
