Cryo-EM structures of KdpFABC suggest a K+ transport mechanism via two inter-subunit half-channels

C. Stock, L. Hielkema, I. Tascón, D. Wunnicke, G. T. Oostergetel, M. Azkargorta, C. Paulino () and I. Hänelt ()
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C. Stock: Goethe University Frankfurt, Max-von-Laue-Straße 9
L. Hielkema: University of Groningen
I. Tascón: Goethe University Frankfurt, Max-von-Laue-Straße 9
D. Wunnicke: Goethe University Frankfurt, Max-von-Laue-Straße 9
G. T. Oostergetel: University of Groningen
M. Azkargorta: Proteomics Platform, CIC bioGUNE, CIBERehd, ProteoRed-ISCIII, Bizkaia Science and Technology Park
C. Paulino: University of Groningen
I. Hänelt: Goethe University Frankfurt, Max-von-Laue-Straße 9

Nature Communications, 2018, vol. 9, issue 1, 1-10

Abstract: Abstract P-type ATPases ubiquitously pump cations across biological membranes to maintain vital ion gradients. Among those, the chimeric K+ uptake system KdpFABC is unique. While ATP hydrolysis is accomplished by the P-type ATPase subunit KdpB, K+ has been assumed to be transported by the channel-like subunit KdpA. A first crystal structure uncovered its overall topology, suggesting such a spatial separation of energizing and transporting units. Here, we report two cryo-EM structures of the 157 kDa, asymmetric KdpFABC complex at 3.7 Å and 4.0 Å resolution in an E1 and an E2 state, respectively. Unexpectedly, the structures suggest a translocation pathway through two half-channels along KdpA and KdpB, uniting the alternating-access mechanism of actively pumping P-type ATPases with the high affinity and selectivity of K+ channels. This way, KdpFABC would function as a true chimeric complex, synergizing the best features of otherwise separately evolved transport mechanisms.

Date: 2018
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DOI: 10.1038/s41467-018-07319-2

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