Supramolecular assembly of chloroplast NAD(P)H dehydrogenase-like complex with photosystem I from Arabidopsis thaliana

Cyclic electron transport/flow (CET/CEF) in chloroplasts is a regulatory mechanism crucial for optimization of plant photosynthetic efficiency. CET is catalyzed by a membrane-embedded NAD(P)H dehydrogenase-like (NDH) complex containing at least 29 protein subunits and associating with photosystem I (PSI) to form the NDH-PSI supercomplex. Here we report the 3.9 [A] resolution structure of Arabidopsis thaliana NDH-PSI (AtNDH-PSI) supercomplex. We have constructed structural models for 26 AtNDH subunits, among which 11 subunits are unique to chloroplast and stabilize the core part of NDH complex. In the supercomplex, one NDH can bind up to two PSI-LHCI complexes at both sides of its membrane arm. Two minor LHCIs, Lhca5 and Lhca6, each present in one PSI-LHCI, interact with NDH and contribute to the supercomplex formation and stabilization. Our results showed structural details of the supercomplex assembly and provide molecular basis for further investigation of the regulatory mechanism of CEF in plants.