Journal Article

Cryo-EM structure of a functional monomeric Photosystem I from Thermosynechococcus elongatus reveals red chlorophyll cluster

Namba Keiichi, Kato Takayuki, Tanaka, Hideaki, Frank, Anna, Gerle Christoph, Kurisu Genji, El-Mohsnawy Eithar, Nowaczyk, Marc M, Çoruh Orkun, Kawamoto Akihiro

2021

Overview

A high-resolution structure of trimeric cyanobacterial Photosystem I (PSI) from Thermosynechococcus elongatus was reported as the first atomic model of PSI almost 20 years ago. However, the monomeric PSI structure has not yet been reported despite long-standing interest in its structure and extensive spectroscopic characterization of the loss of red chlorophylls upon monomerization. Here, we describe the structure of monomeric PSI from Thermosynechococcus elongatus BP-1. Comparison with the trimer structure gave detailed insights into monomerization-induced changes in both the central trimerization domain and the peripheral regions of the complex. Monomerization-induced loss of red chlorophylls is assigned to a cluster of chlorophylls adjacent to PsaX. Based on our findings, we propose a role of PsaX in the stabilization of red chlorophylls and that lipids of the surrounding membrane present a major source of thermal energy for uphill excitation energy transfer from red chlorophylls to P700.Çoruh, Frank et al. report the structure of monomeric Photosystem I from cyanobacteria Thermosynechoccocus elongatus BP-1. They assign monomerization-induced loss of red chlorophylls to a cluster of chlorophylls adjacent to PsaX. This study suggests a role of PsaX in the stabilization of red chlorophylls.

• Publisher: Nature Publishing Group
• Subject: Biology / Chlorophyll / Lipids / Photosystem I / Thermosynechococcus elongatus / Trimers