Figure 6.
Figure 6: Hypothetical mechanism of voltage-dependent gating.
a, Representation of the voltage sensor and S4–S5 linker helix
from the crystal structure (open conformation). Helices are
drawn as ribbons. The view is from the pore, as in Fig. 5, with
the extracellular solution 'above' and the intracellular
solution 'below'. The gating charges (R1 to K5) are shown as
blue sticks. Negatively charged residues in the external and
internal clusters are red; the phenylalanine in the middle is
green. The positively charged residues reach 'outward' towards
the extracellular solution. b, Depiction of a hypothetical
closed conformation of the voltage sensor. The S1 and S2 helices
are hypothesized to maintain their position, whereas the S3–S4
paddle has moved inward. The positive charges on S4 now reach
towards the intracellular solution, and are stabilized through
interactions with the internal negative cluster. The -carbon
position of R1 is adjacent to the phenylalanine, representing a
displacement perpendicular to the plane of the membrane of
approximately 15 Å relative to its location in the open
structure (a). The inward displacement of the S4 helix pushes
down on the N-terminal end of the S4–S5 linker helix, causing
it to tilt towards the intracellular side and to close the pore.
c, Depiction of the open conformation of the S4–S5 linker
helices and pore from the crystal structure. The S4–S5 linker
helices (orange) rest on the S6 helices (blue ribbons) near the
intracellular side. d, A hypothetical model of the S4–S5
linker helices and pore in a closed conformation based on the
crystal structure of a closed potassium channel pore (KcsA, PDB
accession number, 1K4C)^18.
The above figure is reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2007,
450,
376-382)
copyright 2007.
-carbon
position of R1 is adjacent to the phenylalanine, representing a
displacement perpendicular to the plane of the membrane of
approximately 15 Å relative to its location in the open
structure (a). The inward displacement of the S4 helix pushes
down on the N-terminal end of the S4–S5 linker helix, causing
it to tilt towards the intracellular side and to close the pore.
c, Depiction of the open conformation of the S4–S5 linker
helices and pore from the crystal structure. The S4–S5 linker
helices (orange) rest on the S6 helices (blue ribbons) near the
intracellular side. d, A hypothetical model of the S4–S5
linker helices and pore in a closed conformation based on the
crystal structure of a closed potassium channel pore (KcsA, PDB
accession number, 1K4C)^18.