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α-Carboxysome Size Is Controlled by the Disordered Scaffold Protein CsoS2.

ABSTRACT: Carboxysomes are protein microcompartments that function in the bacterial CO₂ concentrating mechanism (CCM) to facilitate CO₂ assimilation. To do so, carboxysomes assemble from thousands of constituent proteins into an icosahedral shell, which encapsulates the enzymes Rubisco and carbonic anhydrase to form structures typically > 100 nm and > 300 megadaltons. Although many of the protein interactions driving the assembly process have been determined, it remains unknown how size and composition are precisely controlled. Here, we show that the size of α-carboxysomes is controlled by the disordered scaffolding protein CsoS2. CsoS2 contains two classes of related peptide repeats that bind to the shell in a distinct fashion, and our data indicate that size is controlled by the relative number of these interactions. We propose an energetic and structural model wherein the two repeat classes bind at the junction of shell hexamers but differ in their preferences for the shell contact angles, and thus the local curvature. In total, this model suggests that a set of specific and repeated interactions between CsoS2 and shell proteins collectively achieve the large size and monodispersity of α-carboxysomes.

SUBMITTER: Oltrogge LM

PROVIDER: S-EPMC10795168 | biostudies-literature | 2024 Jan

REPOSITORIES: biostudies-literature

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α-Carboxysome Size Is Controlled by the Disordered Scaffold Protein CsoS2.

Oltrogge Luke M LM Chen Allen W AW Chaijarasphong Thawatchai T Turnšek Julia B JB Savage David F DF

Biochemistry 20231212 2

Carboxysomes are protein microcompartments that function in the bacterial CO<sub>2</sub> concentrating mechanism (CCM) to facilitate CO<sub>2</sub> assimilation. To do so, carboxysomes assemble from thousands of constituent proteins into an icosahedral shell, which encapsulates the enzymes Rubisco and carbonic anhydrase to form structures typically > 100 nm and > 300 megadaltons. Although many of the protein interactions driving the assembly process have been determined, it remains unknown how s ...[more]

PMID: 38085650

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Project description:Carboxysomes are proteinaceous organelles featuring icosahedral protein shells that enclose the carbon-fixing enzymes, ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco), along with carbonic anhydrase. The intrinsically disordered scaffolding protein CsoS2 plays a vital role in the construction of α-carboxysomes through bridging the shell and cargo enzymes. The N-terminal domain of CsoS2 binds Rubisco and facilitates Rubisco packaging within the α-carboxysome, whereas the C-terminal domain of CsoS2 (CsoS2-C) anchors to the shell and promotes shell assembly. However, the role of the middle region of CsoS2 (CsoS2-M) has remained elusive. Here, we conducted in-depth examinations on the function of CsoS2-M in the assembly of the α-carboxysome shell by generating a series of recombinant shell variants in the absence of cargos. Our results reveal that CsoS2-M assists CsoS2-C in the assembly of the α-carboxysome shell and plays an important role in shaping the α-carboxysome shell through enhancing the association of shell proteins on both the facet-facet interfaces and flat shell facets. Moreover, CsoS2-M is responsible for recruiting the C-terminal truncated isoform of CsoS2, CsoS2A, into α-carboxysomes, which is crucial for Rubisco encapsulation and packaging. This study not only deepens our knowledge of how the carboxysome shell is constructed and regulated but also lays the groundwork for engineering and repurposing carboxysome-based nanostructures for diverse biotechnological purposes.ImportanceCarboxysomes are a paradigm of organelle-like structures in cyanobacteria and many proteobacteria. These nanoscale compartments enclose Rubisco and carbonic anhydrase within an icosahedral virus-like shell to improve CO2 fixation, playing a vital role in the global carbon cycle. Understanding how the carboxysomes are formed is not only important for basic research studies but also holds promise for repurposing carboxysomes in bioengineering applications. In this study, we focuses on a specific scaffolding protein called CsoS2, which is involved in facilitating the assembly of α-type carboxysomes. By deciphering the functions of different parts of CsoS2, especially its middle region, we provide new insights into how CsoS2 drives the stepwise assembly of the carboxysome at the molecular level. This knowledge will guide the rational design and reprogramming of carboxysome nanostructures for many biotechnological applications.

Dataset Information

α-Carboxysome Size Is Controlled by the Disordered Scaffold Protein CsoS2.

Publications

α-Carboxysome Size Is Controlled by the Disordered Scaffold Protein CsoS2.

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