Abstract
NAD(P)H dehydrogenase-like (NDH) complex NDH-1L of cyanobacteria plays a crucial role in cyclic electron flow (CEF) around photosystem I and respiration processes. NDH-1L couples the electron transport from ferredoxin (Fd) to plastoquinone (PQ) and proton pumping from cytoplasm to the lumen that drives the ATP production. NDH-1L-dependent CEF increases the ATP/NADPH ratio, and is therefore pivotal for oxygenic phototrophs to function under stress. Here we report two structures of NDH-1L from Thermosynechococcus elongatus BP-1, in complex with one Fd and an endogenous PQ, respectively. Our structures represent the complete model of cyanobacterial NDH-1L, revealing the binding manner of NDH-1L with Fd and PQ, as well as the structural elements crucial for proper functioning of the NDH-1L complex. Together, our data provides deep insights into the electron transport from Fd to PQ, and its coupling with proton translocation in NDH-1L.
Highlights
NAD(P)H dehydrogenase-like (NDH) complex NDH-1L of cyanobacteria plays a crucial role in cyclic electron flow (CEF) around photosystem I and respiration processes
Light energy is utilized by photosystems I and II (PSI and PSII) to drive the electron transport, which can be classified into two types, the linear electron transport/flow and the cyclic electron transport/ flow[1,2]
We first solved the structure of NDH-1L complex purified from T. elongatus BP-1 (Supplementary Fig. 1) at an overall resolution of 3 Å (Supplementary Fig. 2, Table 1)
Summary
Three lipid molecules were found at the interface between the two arms, facilitating their association (Supplementary Fig. 6d, e) Two of these lipids link the N-helix of NdhI with the membrane domain of NdhA and NdhC (Supplementary Fig. 6d), whereas the third lipid is located in an enclosed cavity formed by the N-terminal fragments from NdhL, NdhN, and NdhK (Supplementary Fig. 6e). Several OPS subunits, including NdhS, NdhO, and NdhV, were previously suggested to be involved in Fd binding[32,34,36] Neither of these subunits directly interact with Fd as shown in our NDH-Fd structure, whereas two conserved subunits, NdhI and NdhH, form extensive contacts with Fd. The long hairpin loop of NdhI, together with a Cterminal fragment from NdhH, shapes a positively-charged patch on the surface of NDH-1L complex, and forms strong electronic interactions with the acidic residues of Fd (Fig. 4a–c), is essential for Fd binding. In addition to the β1-2 loop of NdhH, the TMH5–6 loop
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