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Structural Biology 2018 & STD AIDS 2018
Journal of Genetics and Molecular Biology
|
Volume 2
S e p t e m b e r 0 3 - 0 4 , 2 0 1 8 | B a n g k o k , T h a i l a n d
allied
academies
STD-AIDS AND INFECTIOUS DISEASES
STRUCTURAL BIOLOGY AND PROTEOMICS
&
International Conference on
International Conference on
Joint Event on
J Genet Mol Biol 2018, Volume 2
STRUCTURAL BASIS FOR LIPID-DEPENDENT GATING OF A KV CHANNEL
Qiu-Xing Jiang
University of Florida, USA
L
ipid-dependent gating refers to our observations that lipid molecules without phosphate groups in their headgroup regions,
called nonphospholipids, favor the resting state of the voltage-sensor domain in a voltage-gated potassium (Kv) channel
whereas phospholipid molecules favor the activated state. More studies suggest that the annular lipids and a Kv channel form a
functional unit and both nonspecific and specific interactions at the protein-lipid interface contribute to the energetic differences
of the channel in different gating states. Since our discovery of the phenomenon in KvAP, similar results have been obtained from
other voltage-gated ion channels in both
in vitro
and
ex vivo
systems, suggesting that the lipid-dependent gating could be a more
generic gating mode for other voltage-gated ion channels. To analyze the conformational changes of a Kv channel in different
lipids, we obtained a peptide-binder that recognizes a non-phospholipid-stabilized resting state of the KvAP voltage sensor and
found that attachment of the peptide to the C-terminus of the channel appears to keep it in the resting state in phospholipid
membranes. We analyzed the structure of the KvAP-peptide fusion protein by single particle cryoEM and revealed a voltage-
sensor ring that may keep the voltage-sensor paddle in a resting state where all its arginine residues face the intracellular side
of the gating pore with the tip of the S3S4 paddle leaning against the splayed-open S1/S2. The structural features of the new
model are different from the four-helix bundle structure of the voltage sensor domain in the activated conformation and allow
the S3/S4 to face annular lipids directly. Such structural arrangements could explain a set of biochemical data we obtained
from different channel mutants and reveal new insights on the possible movement of the voltage sensor domain to achieve its
gating control of the ion-conducting pore. Another surprise from the cryoEM study is that an unknown protein binds tightly to
the extracellular side of the KvAP pore domain. MS spectrometry and proteomic analysis suggested a few candidates that need
further characterization. We are investigating whether the new pore-binders play a role in the lipid or voltage-dependent gating
of the channel.