9WYP

The PSI-ACPI supercomplex from the cryptophyte Chroomonas placoidea

Summary for 9WYP

• Entry DOI: 10.2210/pdb9wyp/pdb
• EMDB information: 66373
• Descriptor: ACPI-1, Photosystem I P700 chlorophyll a apoprotein A1, Photosystem I P700 chlorophyll a apoprotein A2, ... (40 entities in total)
• Functional Keywords: photosynthesis, structural protein
• Biological source: Chroomonas placoidea; More
• Total number of polymer chains: 29
• Total formula weight: 1005737.22

Authors

Li, X.Y.,Mao, Z.Y.,Han, G.Y. (deposition date: 2025-09-27, release date: 2026-01-07)

Primary citation

Li, X.,Mao, Z.,Li, Z.,Shen, L.,Li, X.,Yang, Y.,Wang, W.,Kuang, T.,Shen, J.R.,Han, G.
Structural insights into a PSI-ACPI supercomplex from a cryptophyte alga Chroomonas placoidea.
Photosynth.Res., 164:2-2, 2025

PubMed Abstract: Cryptophyte algae are an important group of photosynthetic eukaryotes and originated evolutionarily from a secondary endosymbiosis with a red algal ancestor. Photosystem I (PSI) of cryptophyte algae binds alloxanthin-chlorophyll a/c-binding proteins (ACPs) equivalent to the light harvesting complexes (LHCs) of green algae and higher plants. Here, we report a high resolution (2.25 Å) structure of the PSI-ACPI supercomplex purified from the cryptophyte Chroomonas placoidea (C. placoidea) by cryo-electron microscopy. The PSI-ACPI supercomplex consists of a monomeric PSI core, 14 ACPI subunits and a Chl-binding subunit, CCPI-S. The 14 ACPI subunits are divided into two layers, with an inner layer including 11 ACPIs, and an outer layer consisting of 3 ACPIs. The CCPI-S mediates the connections and energy transfer between the outer and inner ACPI layers. Due to the current higher resolution, a unique PsaQ subunit bound at the lumenal side was identified in the PSI core. Two new pigment molecules Chl a856PsaA and Mon 627ACPI − 8 as well as 18 new lipids were identified, compared to the previously reported PSI-ACPI structure from the cryptophyte alga C. placoidea (Zhao et al. 2023). These lipids mediate the interactions of subunits and the assembly of PSI-ACPI. These results provide structural insights for the assembly of the PSI-ACPI complex and pathways of light-energy absorption and transfer in cryptophyte PSI-ACPI, as well as the possible adaptation mechanisms to fluctuating light conditions.

PubMed: 41420767
DOI: 10.1007/s11120-025-01191-0

Experimental method

ELECTRON MICROSCOPY (2.25 Å)