Scaffolding proteins guide the evolution of algal light harvesting antennas

• DOI: 10.1038/s41467-021-22128-w
• Publication Date: 2021-03-25T11:06:58Z
• Authors: Harry W. Rathbone; Katharine A. Michie; Michael J. Landsberg; Beverley R. Green; Paul M. G. Curmi
• Keywords: Phycobilisome; Phycobiliprotein; Phycoerythrin; Red algae

Abstract Photosynthetic organisms have developed diverse antennas composed of chromophorylated proteins to increase photon capture. Cryptophyte algae acquired their photosynthetic organelles (plastids) from a red alga by secondary endosymbiosis. Cryptophytes lost the primary algal antenna, phycobilisome, replacing it with unique antenna αβ protomers, where β subunit originates phycobilisome. The origin cryptophyte particularly α subunit, is unknown. Here we show that evolved complex between scaffolding protein and phycoerythrin β. Published cryo-EM maps for two phycobilisomes contain clusters unmodelled density homologous cryptophyte-αβ protomer. We modelled these densities, identifying new family related phycobilisome linker possess multiple copies cryptophyte-α-like domain. These domains bind to, stabilise, conserved hydrophobic surface on β, which same binding site its partner in α. propose after endosymbiosis outcompeted resulting demise emergence antenna.