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

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

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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