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Publication Abstract from PubMed

Light-harvesting 2 (LH2) antenna complexes augment the collection of solar energy in many phototrophic bacteria. Despite its frequent role as a model for such complexes, there has been no three-dimensional (3D) structure available for the LH2 from the purple phototroph Rhodobacter sphaeroides. We used cryo-electron microscopy (cryo-EM) to determine the 2.1 A resolution structure of this LH2 antenna, which is a cylindrical assembly of nine alphabeta heterodimer subunits, each of which binds three bacteriochlorophyll a (BChl) molecules and one carotenoid. The high resolution of this structure reveals all of the interpigment and pigment-protein interactions that promote the assembly and energy-transfer properties of this complex. Near the cytoplasmic face of the complex there is a ring of nine BChls, which absorb maximally at 800 nm and are designated as B800; each B800 is coordinated by the N-terminal carboxymethionine of LH2-alpha, part of a network of interactions with nearby residues on both LH2-alpha and LH2-beta and with the carotenoid. Nine carotenoids, which are spheroidene in the strain we analyzed, snake through the complex, traversing the membrane and interacting with a ring of 18 BChls situated toward the periplasmic side of the complex. Hydrogen bonds with C-terminal aromatic residues modify the absorption of these pigments, which are red-shifted to 850 nm. Overlaps between the macrocycles of the B850 BChls ensure rapid transfer of excitation energy around this ring of pigments, which act as the donors of energy to neighboring LH2 and reaction center light-harvesting 1 (RC-LH1) complexes.

Cryo-EM Structure of the Rhodobacter sphaeroides Light-Harvesting 2 Complex at 2.1 A.,Qian P, Swainsbury DJK, Croll TI, Castro-Hartmann P, Divitini G, Sader K, Hunter CN Biochemistry. 2021 Nov 9;60(44):3302-3314. doi: 10.1021/acs.biochem.1c00576. Epub , 2021 Oct 26. PMID:34699186^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.