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-Structure paper
Title | Cryo-EM structures of light-harvesting 2 complexes from reveal the molecular origin of absorption tuning. |
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Journal, issue, pages | Proc Natl Acad Sci U S A, Vol. 119, Issue 43, Page e2210109119, Year 2022 |
Publish date | Oct 25, 2022 |
![]() | Pu Qian / Cam T Nguyen-Phan / Alastair T Gardiner / Tristan I Croll / Aleksander W Roszak / June Southall / Philip J Jackson / Cvetelin Vasilev / Pablo Castro-Hartmann / Kasim Sader / C Neil Hunter / Richard J Cogdell / ![]() ![]() |
PubMed Abstract | The genomes of some purple photosynthetic bacteria contain a multigene family encoding a series of α- and β-polypeptides that together form a heterogeneous antenna of light-harvesting 2 (LH2) ...The genomes of some purple photosynthetic bacteria contain a multigene 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 deletion mutants in , each encoding a single type of 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. |
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Methods | EM (single particle) |
Resolution | 2.7 - 3.6 Å |
Structure data | EMDB-14633, PDB-7zcu: EMDB-14650, PDB-7zdi: EMDB-14682, PDB-7ze3: EMDB-14685, PDB-7ze8: |
Chemicals | ![]() ChemComp-BCL: ![]() ChemComp-IRM: ![]() ChemComp-HOH: ![]() ChemComp-ZE0: |
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