Structure of the potassium-importing KdpFABC membrane complex
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Figure: The structure of KdpFABC shown with green KdpA,
brown/red KdpB, purple KdpC and olive KdpF. |
David Stokes group (New York University)
The group of David Stokes at New York University
published the structure of an intriguing membrane-spanning ion pump.
In order to survive at very low K+ concentrations, bacteria
have evolved the high-affinity, inducible Kdp system that functions as
a primary active transporter. KdpFABC is a heterotetrameric membrane
complex that uses ATP to pump K+ into the cell in an
unprecedented partnership between a channel-like subunit (KdpA) and a
pump-like subunit (KdpB). KdpA belongs to the superfamily of
K+ transporters and KdpB is a P-type ATPase, but both
subunits have been repurposed in the Kdp complex. KdpB is a P-type
ATPase that does not pump, but rather uses ATP-driven conformational
changes to control KdpA. KdpA has been adapted to move ions against an
electro-chemical potential. The structure hints at how this process
works. In particular, a kinked helix (cyan) in KdpA is coupled to the
KdpB catalytic domain (dark red), which may control the cytoplasmic
gate to the K+ transport pathway. A tunnel (blue) buried
within the membrane domain links the KdpA selectivity filter (occupied
by K+) and the KdpB canonical cation binding site (occupied
by a water molecule). Stokes and colleagues have proposed that charge
is transferred through this tunnel by a water wire, thus coupling ion
binding within KdpA to ATP hydrolysis by KdpB and inducing
conformational changes that lead to the translocation of K+
across the membrane.
Citation: Huang, C-S, Pedersen, BP, Stokes, DL
Crystal structure of the potassium-importing KdpFABC membrane complex,
Nature 546, 681-685 (2017). DOI: 10.1038/nature22970
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