Helical allophycocyanin nanotubes absorb far-red light in a thermophilic cyanobacterium

  • Sci Adv. 2023 Mar 24;9(12):eadg0251. doi: 10.1126/sciadv.adg0251.
Christopher J Gisriel  1 ,  Eduard Elias  2 ,  Gaozhong Shen  3 ,  Nathan T Soulier  3 ,  David A Flesher  4 ,  M R Gunner  5 ,  Gary W Brudvig  1  4 ,  Roberta Croce  2 ,  Donald A Bryant  3
Affiliations
  • 1. Department of Chemistry, Yale University, New Haven, CT 06520, USA.
  • 2. Department of Physics and Astronomy, and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
  • 3. Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
  • 4. Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA.
  • 5. Department of Physics, City College of New York, New York, NY 10031, USA.
PMID: 36961897 DOI: 10.1126/sciadv.adg0251
Abstract

To compete in certain low-light environments, some cyanobacteria express a paralog of the light-harvesting phycobiliprotein, allophycocyanin (AP), that strongly absorbs far-red light (FRL). Using cryo-electron microscopy and time-resolved absorption spectroscopy, we reveal the structure-function relationship of this FRL-absorbing AP complex (FRL-AP) that is expressed during acclimation to low light and that likely associates with chlorophyll a-containing photosystem I. FRL-AP assembles as helical nanotubes rather than typical toroids due to alterations of the domain geometry within each subunit. Spectroscopic characterization suggests that FRL-AP nanotubes are somewhat inefficient antenna; however, the enhanced ability to harvest FRL when visible light is severely attenuated represents a beneficial trade-off. The results expand the known diversity of light-harvesting proteins in nature and exemplify how biological plasticity is achieved by balancing resource accessibility with efficiency.

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