 |
PDBsum entry 3e8h
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Membrane protein
|
PDB id
|
|
|
|
3e8h
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Structural analysis of ion selectivity in the nak channel.
|
|
|
Authors
|
|
A.Alam,
Y.Jiang.
|
|
|
Ref.
|
|
Nat Struct Biol, 2009,
16,
35-41.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Here we present a detailed characterization of ion binding in the NaK pore using
the high-resolution structures of NaK in complex with various cations. These
structures reveal four ion binding sites with similar chemical environments but
vastly different ion preference. The most nonselective of all is site 3, which
is formed exclusively by backbone carbonyl oxygen atoms and resides deep within
the selectivity filter. Additionally, four water molecules in combination with
four backbone carbonyl oxygen atoms are seen to participate in K(+) and Rb(+)
ion chelation, at both the external entrance and the vestibule of the NaK
filter, confirming the channel's preference for an octahedral ligand
configuration for K(+) and Rb(+) binding. In contrast, Na(+) binding in the NaK
filter, particularly at site 4, utilizes a pyramidal ligand configuration that
requires the participation of a water molecule in the cavity. Therefore, the
ability of the NaK filter to bind both Na(+) and K(+) ions seemingly arises from
the ions' ability to use the existing environment in unique ways, rather than
from any structural rearrangements of the filter itself.
|
|
|
|
|
|
|
|
Figure 2.
(a,b) The 2F[o] – F[c] ion omit maps (1.5  )
show electron density of ion binding in the K^+ complex (a) and
Rb^+ complex (b) of NaKN  19.
K^+ and Rb^+ ions are colored green, with water molecules
represented as red spheres. (c) The maintenance of an octahedral
ligand arrangement in the K^+ complex, which also holds true for
the Rb^+ complex. Oxygen atoms from the front and back subunits
chelating the ions are shown as red spheres. (d) F[Cs soak] –
F[K] difference map contoured at 10 ,
showing Cs^+ binding at site 3.
|
|
Figure 4.
(a) F[Ba soak] – F[K] difference map (blue mesh) contoured
at 10 showing
the two Ba^2+ binding sites. (b) 2F[o] – F[c] ion omit maps of
a Ba^2+-soaked crystal contoured at 1.5 .
The electron density at the external entrance and site 3 was
modeled as Ba^2+ (orange spheres), and water molecules are
modeled as red spheres. (c) Ba^2+ (left) and Ca^2+ (right)
blocking of ^86Rb influx in liposomes loaded with NaCl.
|
|
|
|
|
|
The above figures are
reprinted
from an Open Access publication published by Macmillan Publishers Ltd:
Nat Struct Biol
(2009,
16,
35-41)
copyright 2009.
|
|
|
|
|
|
|
