Carboxysomes: metabolic modules for CO2 fixation

Abstract

The carboxysome is a bacterial microcompartment encapsulating the enzymes carbonic anhydrase and ribulose-1,5-bisphosphate carboxylase/oxygenase. As the site of CO2 fixation, it serves an essential role in the carbon dioxide concentrating mechanism of many chemoautotrophs and all cyanobacteria. Carboxysomes and other bacterial microcompartments self-assemble through specific protein-protein interactions that are typically mediated by conserved protein domains. In this review, we frame our current understanding of carboxysomes in the context of their component protein domains with their inherent function as the 'building blocks' of carboxysomes. These building blocks are organized in genetic modules (conserved chromosomal loci) that encode for carboxysomes and ancillary proteins essential for the integration of the organelle with the rest of cellular metabolism. This conceptual framework provides the foundation for 'plug-and-play' engineering of carboxysomes as CO2 fixation modules in a variety of biotechnological applications.

Bacterial microcompartments

“…There is currently only one known example of an anabolic BMC — the carboxysome 2–4 — which is found in all cyanobacteria and in some chemotrophic bacteria. Carboxysomes contain the enzymes carbonic anhydrase 10 [G] and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) [G] and function to fix carbon dioxide as part of the Calvin-Benson–Bassham cycle [G] (Figure 1A).…”

Dual Role of a Rubisco Activase in Metabolic Repair and Carboxysome Organization

“…A distinguishing feature is the presence of a Rubisco small subunitlike (SSUL) domain, connected to the C-terminus of the AAA+ core via a flexible linker (Lechno-Yossef et al, 2020) (Figure 1A). In cyanobacteria, Rubisco is packaged together with carbonic anhydrase into carboxysomes, membraneless compartments in which high concentrations of CO2 are generated for carbon fixation (Badger and Price, 2003;Price et al, 1998;Turmo et al, 2017). The scaffolding protein CcmM of β-carboxysomes utilizes multiple SSUL modules to induce Rubisco condensate formation during carboxysome biogenesis (Long et al, 2010;Wang et al, 2019).…”

Biotechnological Advances in Bacterial Microcompartment Technology

“…There are two basic types of BMCs reflecting their participation in anabolic or catabolic processes, which are termed carboxysomes and metabolosomes respectively ( Figure 1) [2]. The anabolic carboxysomes are involved in carbon fixation, utilising an encapsulated carbonic anhydrase and ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) ( Figure 1) [6,7]. Carboxysomes are divided into two distinct classes that are named according to the form of encapsulated RuBisCO, with α-carboxysomes containing 1A RuBisCO and β-carboxysomes containing 1B RuBisCO.…”