Issue 22, 2024

An integrated approach towards extracting structural characteristics of chlorosomes from a bchQ mutant of Chlorobaculum tepidum

Abstract

Chlorosomes, the photosynthetic antenna complexes of green sulfur bacteria, are paradigms for light-harvesting elements in artificial designs, owing to their efficient energy transfer without protein participation. We combined magic angle spinning (MAS) NMR, optical spectroscopy and cryogenic electron microscopy (cryo-EM) to characterize the structure of chlorosomes from a bchQ mutant of Chlorobaculum tepidum. The chlorosomes of this mutant have a more uniform composition of bacteriochlorophyll (BChl) with a predominant homolog, [8Ethyl, 12Ethyl] BChl c, compared to the wild type (WT). Nearly complete 13C chemical shift assignments were obtained from well-resolved homonuclear 13C–13C RFDR data. For proton assignments heteronuclear 13C–1H (hCH) data sets were collected at 1.2 GHz spinning at 60 kHz. The CHHC experiments revealed intermolecular correlations between 132/31, 132/32, and 121/31, with distance constraints of less than 5 Å. These constraints indicate the synanti parallel stacking motif for the aggregates. Fourier transform cryo-EM data reveal an axial repeat of 1.49 nm for the helical tubular aggregates, perpendicular to the inter-tube separation of 2.1 nm. This axial repeat is different from WT and is in line with BChl synanti stacks running essentially parallel to the tube axis. Such a packing mode is in agreement with the signature of the Qy band in circular dichroism (CD). Combining the experimental data with computational insight suggests that the packing for the light-harvesting function is similar between WT and bchQ, while the chirality within the chlorosomes is modestly but detectably affected by the reduced compositional heterogeneity in bchQ.

Graphical abstract: An integrated approach towards extracting structural characteristics of chlorosomes from a bchQ mutant of Chlorobaculum tepidum

Supplementary files

Article information

Article type
Paper
Submitted
17 Jan 2024
Accepted
05 Mar 2024
First published
28 Mar 2024
This article is Open Access
Creative Commons BY-NC license

Phys. Chem. Chem. Phys., 2024,26, 15856-15867

An integrated approach towards extracting structural characteristics of chlorosomes from a bchQ mutant of Chlorobaculum tepidum

L. Dsouza, X. Li, V. Erić, A. Huijser, T. L. C. Jansen, A. R. Holzwarth, F. Buda, D. A. Bryant, S. Bahri, K. B. S. S. Gupta, G. J. A. Sevink and H. J. M. de Groot, Phys. Chem. Chem. Phys., 2024, 26, 15856 DOI: 10.1039/D4CP00221K

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