The PufX quinone channel enables the light-harvesting 1 antenna to bind more carotenoids for light collection and photoprotection

Photosynthesis in some phototrophic bacteria requires the PufX component of the reaction centre-light-harvesting 1-PufX (RC-LH1-PufX) complex, which creates a pore for quinone/quinol (Q/QH2 ) exchange across the LH1 barrier surrounding the RC. However, photosynthetic bacteria such as Thermochromatium (T.) tepidum do not require PufX because there are fewer carotenoid binding sites, creating multiple pores in the LH1 ring for Q/QH2 exchange. We show that an αTrp-24 →Phe alteration of the Rhodobacter (Rba.) sphaeroides LH1 antenna impairs carotenoid binding and allows photosynthetic growth in the absence of PufX. We propose that acquisition of PufX and confining Q/QH2 traffic to a pore adjacent to the RC QB site is an evolutionary upgrade that allows increased LH1 carotenoid content for enhanced light absorption and photoprotection. This article is protected by copyright. All rights reserved.