Molecular structures reveal the origin of spectral variation in cryptophyte light harvesting antenna proteins

Author:

Michie Katharine A.123,Harrop Stephen J.14,Rathbone Harry W.12,Wilk Krystyna E.1,Teng Chang Ying5,Hoef‐Emden Kerstin6,Hiller Roger G.7,Green Beverley R.5,Curmi Paul M. G.12ORCID

Affiliation:

1. School of Physics The University of New South Wales Sydney New South Wales Australia

2. School of Biotechnology and Biomolecular Sciences The University of New South Wales Sydney New South Wales Australia

3. Mark Wainwright Analytical Centre University of New South Wales Sydney New South Wales Australia

4. MX Beamlines, Australian Synchrotron Clayton Victoria Australia

5. Department of Botany University of British Columbia Vancouver Canada

6. Botanical Institute University of Cologne Cologne Germany

7. Department of Biological Sciences Macquarie University Sydney New South Wales Australia

Abstract

AbstractIn addition to their membrane‐bound chlorophyll a/c light‐harvesting antenna, the cryptophyte algae have evolved a unique phycobiliprotein antenna system located in the thylakoid lumen. The basic unit of this antenna consists of two copies of an αβ protomer where the α and β subunits scaffold different combinations of a limited number of linear tetrapyrrole chromophores. While the β subunit is highly conserved, encoded by a single plastid gene, the nuclear‐encoded α subunits have evolved diversified multigene families. It is still unclear how this sequence diversity results in the spectral diversity of the mature proteins. By careful examination of three newly determined crystal structures in comparison with three previously obtained, we show how the α subunit amino acid sequences control chromophore conformations and hence spectral properties even when the chromophores are identical. Previously we have shown that α subunits control the quaternary structure of the mature αβ.αβ complex (either open or closed), however, each species appeared to only harbor a single quaternary form. Here we show that species of the Hemiselmis genus contain expressed α subunit genes that encode both distinct quaternary structures. Finally, we have discovered a common single‐copy gene (expressed into protein) consisting of tandem copies of a small α subunit that could potentially scaffold pairs of light harvesting units. Together, our results show how the diversity of the multigene α subunit family produces a range of mature cryptophyte antenna proteins with differing spectral properties, and the potential for minor forms that could contribute to acclimation to varying light regimes.

Funder

Asian Office of Aerospace Research and Development

Australian Research Council

Natural Sciences and Engineering Research Council of Canada

Publisher

Wiley

Subject

Molecular Biology,Biochemistry

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