Rubisco accumulation factor 1 (Raf1) plays essential roles in mediating Rubisco assembly and carboxysome biogenesis

Huang, Fang, Kong, Wen-Wen, Sun, Yaqi, Chen, Taiyu, Dykes, Gregory F ORCID: 0000-0002-0626-9487, Jiang, Yong-Liang and Liu, Lu-Ning ORCID: 0000-0002-8884-4819 (2020) Rubisco accumulation factor 1 (Raf1) plays essential roles in mediating Rubisco assembly and carboxysome biogenesis. Proceedings of the National Academy of Sciences of the United States of America, 117 (29). pp. 17418-17428.

Text
2020_9_Raf1_PNAS.pdf - Published version
Download (3MB) | Preview

Official URL: https://www.pnas.org/content/117/29/17418

Abstract

Carboxysomes are membrane-free organelles for carbon assimilation in cyanobacteria. The carboxysome consists of a proteinaceous shell that structurally resembles virus capsids and internal enzymes including ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), the primary carbon-fixing enzyme in photosynthesis. The formation of carboxysomes requires hierarchical self-assembly of thousands of protein subunits, initiated from Rubisco assembly and packaging to shell encapsulation. Here we study the role of Rubisco assembly factor 1 (Raf1) in Rubisco assembly and carboxysome formation in a model cyanobacterium, Synechococcus elongatus PCC7942 (Syn7942). Cryo-electron microscopy reveals that Raf1 facilitates Rubisco assembly by mediating RbcL dimer formation and dimer–dimer interactions. Syn7942 cells lacking Raf1 are unable to form canonical intact carboxysomes but generate a large number of intermediate assemblies comprising Rubisco, CcaA, CcmM, and CcmN without shell encapsulation and a low abundance of carboxysome-like structures with reduced dimensions and irregular shell shapes and internal organization. As a consequence, the Raf1-depleted cells exhibit reduced Rubisco content, CO2-fixing activity, and cell growth. Our results provide mechanistic insight into the chaperone-assisted Rubisco assembly and biogenesis of carboxysomes. Advanced understanding of the biogenesis and stepwise formation process of the biogeochemically important organelle may inform strategies for heterologous engineering of functional CO2-fixing modules to improve photosynthesis.

Item Type:	Article
Uncontrolled Keywords:	Rubisco accumulation factor 1, Rubisco, carboxysome, carbon fixation, cyanobacteria
Depositing User:	Symplectic Admin
Date Deposited:	14 Jul 2020 08:12
Last Modified:	18 Jan 2023 23:46
DOI:	10.1073/pnas.2007990117
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3093918