Fig. 4: The salt bridge and NdhP, Q jointly stabilize photosynthetic NDH-1.

a The NdhP and NdhQ subunits are exhibited in the predicted structures of photosynthetic NDH-1 in Synechocystis 6803 by AlphaFold-Multimer. NdhP and NdhQ are highlighted in deep sky blue and red, respectively, and NdhD1 is displayed as blue. b A close-up view of the black box in (a) shows that the NdhP and NdhQ subunits exclusively interact with the NdhD1 subunit. Synechocystis 6803 cells were cultured under a light intensity of 40 µmol photons m⁻² s⁻¹ with 2% CO₂ in air and harvested during the logarithmic growth phase for experiments (c, d). c, d The disruption of the salt bridge in the NdhP or NdhQ-deletion mutant destabilizes photosynthetic NDH-1. c Thylakoid protein complexes isolated from the wild type (WT) Synechocystis 6803 and its double mutants were separated by BN-PAGE. Thylakoid membrane extract corresponding to 9 µg of chlorophyll a was loaded onto each lane. d Protein complexes were electroblotted to a polyvinylidene difluoride membrane, and the membrane was cross-reacted with anti-NdhI, -NdhK, and -NdhM to probe the assembly of the NDH-1L and NDH-1M complexes. Red and blue arrows indicate the locations of the NDH-1L and NDH-1M complexes, respectively.