Scaffolding protein CcmM directs multiprotein phase separation in \u03b2-carboxysome biogenesis

Kun Zang,F Ulrich Hartl,Huping Wang,Manajit Hayer-Hartl

doi:10.1038/s41594-021-00676-5

Kun Zang, F Ulrich Hartl + Show 2 more

Open Access

https://doi.org/10.1038/s41594-021-00676-5

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Abstract

Carboxysomes in cyanobacteria enclose the enzymes Rubisco and carbonic anhydrase to optimize photosynthetic carbon fixation. Understanding carboxysome assembly has implications in agricultural biotechnology. Here we analyzed the role of the scaffolding protein CcmM of the β-cyanobacterium Synechococcus elongatus PCC 7942 in sequestrating the hexadecameric Rubisco and the tetrameric carbonic anhydrase, CcaA. We find that the trimeric CcmM, consisting of γCAL oligomerization domains and linked small subunit-like (SSUL) modules, plays a central role in mediation of pre-carboxysome condensate formation through multivalent, cooperative interactions. The γCAL domains interact with the C-terminal tails of the CcaA subunits and additionally mediate a head-to-head association of CcmM trimers. Interestingly, SSUL modules, besides their known function in recruiting Rubisco, also participate in intermolecular interactions with the γCAL domains, providing further valency for network formation. Our findings reveal the mechanism by which CcmM functions as a central organizer of the pre-carboxysome multiprotein matrix, concentrating the core components Rubisco and CcaA before β-carboxysome shell formation.

Highlights

Carboxysomes in cyanobacteria enclose the enzymes Rubisco and carbonic anhydrase to optimize photosynthetic carbon fixation
NATURE STRUCTURAL & MOLECULAR BIOLOgy turbidity was detected for either protein alone (Fig. 1d,e), a strong turbidity signal was observed when M58 and CcaA were combined (Fig. 1d–f), consistent with condensate formation
Discussion β-Carboxysome biogenesis involves the sequestration of Rubisco together with the carbonic anhydrase CcaA, followed by shell formation[55]

Summary

Introduction

Carboxysomes in cyanobacteria enclose the enzymes Rubisco and carbonic anhydrase to optimize photosynthetic carbon fixation. Data Fig. 2d), suggesting that the C2 sequence mediates the interaction of CcaA with the γCAL domains of M58 No turbidity signal was detectable with CCTRIM35, even at high concentrations and low salt (Extended Data Fig. 4h), pointing to an interaction of SSUL modules with the γCAL domains in M58 and not between SSUL modules.

Results

Conclusion