Download MendeleyCryo-EM structures of light-harvesting 2 complexes from Rhodopseudomonas palustris reveal the molecular origin of absorption tuning.
Qian, P., Nguyen-Phan, C.T., Gardiner, A.T., Croll, T.I., Roszak, A.W., Southall, J., Jackson, P.J., Vasilev, C., Castro-Hartmann, P., Sader, K., Hunter, C.N., Cogdell, R.J.(2022) Proc Natl Acad Sci U S A 119: e2210109119-e2210109119
- PubMed: 36251992
- DOI: https://doi.org/10.1073/pnas.2210109119
- Primary Citation of Related Structures:
7ZCU, 7ZDI, 7ZE3, 7ZE8 - PubMed Abstract:
The genomes of some purple photosynthetic bacteria contain a multigene puc family encoding a series of α- and β-polypeptides that together form a heterogeneous antenna of light-harvesting 2 (LH2) complexes. To unravel this complexity, we generated four sets of puc deletion mutants in Rhodopseudomonas palustris , each encoding a single type of pucBA gene pair and enabling the purification of complexes designated as PucA-LH2, PucB-LH2, PucD-LH2, and PucE-LH2. The structures of all four purified LH2 complexes were determined by cryogenic electron microscopy (cryo-EM) at resolutions ranging from 2.7 to 3.6 Å. Uniquely, each of these complexes contains a hitherto unknown polypeptide, γ, that forms an extended undulating ribbon that lies in the plane of the membrane and that encloses six of the nine LH2 αβ-subunits. The γ-subunit, which is located near to the cytoplasmic side of the complex, breaks the C9 symmetry of the LH2 complex and binds six extra bacteriochlorophylls (BChls) that enhance the 800-nm absorption of each complex. The structures show that all four complexes have two complete rings of BChls, conferring absorption bands centered at 800 and 850 nm on the PucA-LH2, PucB-LH2, and PucE-LH2 complexes, but, unusually, the PucD-LH2 antenna has only a single strong near-infared (NIR) absorption peak at 803 nm. Comparison of the cryo-EM structures of these LH2 complexes reveals altered patterns of hydrogen bonds between LH2 αβ-side chains and the bacteriochlorin rings, further emphasizing the major role that H bonds play in spectral tuning of bacterial antenna complexes.
Organizational Affiliation:
Materials and Structure Analysis, Thermofisher Scientific, Eindhoven, 5651 GG The Netherlands.
