Photoprotective mechanisms have evolved in photosynthetic organisms to cope with fluctuating light conditions. Under high irradiance, the production of dangerous oxygen species is stimulated and ...causes photo-oxidative stress. One of these photoprotective mechanisms, non photochemical quenching (qE), decreases the excess absorbed energy arriving at the reaction centers by increasing thermal dissipation at the level of the antenna. In this review we describe results leading to the discovery of this process in cyanobacteria (qE
cya), which is mechanistically distinct from its counterpart in plants, and recent progress in the elucidation of this mechanism. The cyanobacterial photoactive soluble orange carotenoid protein is essential for the triggering of this photoprotective mechanism. Light induces structural changes in the carotenoid and the protein leading to the formation of a red active form. The activated red form interacts with the phycobilisome, the cyanobacterial light-harvesting antenna, and induces a decrease of the phycobilisome fluorescence emission and of the energy arriving to the reaction centers. The orange carotenoid protein is the first photoactive protein to be identified that contains a carotenoid as the chromophore. Moreover, its photocycle is completely different from those of other photoactive proteins. A second protein, called the Fluorescence Recovery Protein encoded by the
slr1964 gene in
Synechocystis PCC 6803, plays a key role in dislodging the red orange carotenoid protein from the phycobilisome and in the conversion of the free red orange carotenoid protein to the orange, inactive, form. This protein is essential to recover the full antenna capacity under low light conditions after exposure to high irradiance. This article is part of a Special Issue entitled: Photosystem II.
► We describe a photoprotective energy dissipating mechanism in cyanobacteria. ► This mechanism decreases the energy arriving at the reaction centers. ► The orange carotenoid protein is the inducer of energy dissipation. ► Energy dissipation occurs at the level of phycobilisomes. ► The Fluorescence Recovery Protein is essential to decrease energy dissipation.
Bacterial Microcompartments (BMCs) are used by diverse bacteria to compartmentalize enzymatic reactions, functioning analogously to the organelles of eukaryotes. The bounding membrane and ...encapsulated components are composed entirely of protein, which makes them ideal targets for modification by genetic engineering. In contrast to viruses, in which generally only one protein forms the capsid, the shells of BMCs consist of a variety of shell proteins, each a potential unit of selection. Despite their differences in permeability, the shell proteins are surprisingly interchangeable. Recent developments have shown that they are also highly amenable to engineered modifications which poise them for a variety of biotechnological applications. Given their modular structure, with a module defined as a semi-autonomous functional unit, BMCs can be considered apps for programming metabolism that can be de-bugged by adaptive evolution.
Bacterial Microcompartments (BMCs) are proteinaceous organelles that encapsulate critical segments of autotrophic and heterotrophic metabolic pathways; they are functionally diverse and are found ...across 23 different phyla. The majority of catabolic BMCs (metabolosomes) compartmentalize a common core of enzymes to metabolize compounds via a toxic and/or volatile aldehyde intermediate. The core enzyme phosphotransacylase (PTAC) recycles Coenzyme A and generates an acyl phosphate that can serve as an energy source. The PTAC predominantly associated with metabolosomes (PduL) has no sequence homology to the PTAC ubiquitous among fermentative bacteria (Pta). Here, we report two high-resolution PduL crystal structures with bound substrates. The PduL fold is unrelated to that of Pta; it contains a dimetal active site involved in a catalytic mechanism distinct from that of the housekeeping PTAC. Accordingly, PduL and Pta exemplify functional, but not structural, convergent evolution. The PduL structure, in the context of the catalytic core, completes our understanding of the structural basis of cofactor recycling in the metabolosome lumen.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Microbes often augment their metabolism by conditionally constructing proteinaceous organelles, known as bacterial microcompartments (BMCs), that encapsulate enzymes to degrade organic compounds or ...assimilate CO2. BMCs self-assemble and are spatially delimited by a semi-permeable shell made up of hexameric, trimeric, and pentameric shell proteins. Bioengineers aim to recapitulate the organization and efficiency of these complex biological architectures by redesigning the shell to incorporate non-native enzymes from biotechnologically relevant pathways. To meet this challenge, a diverse set of synthetic biology tools are required, including methods to manipulate the properties of the shell as well as target and organize cargo encapsulation. We designed and determined the crystal structure of a synthetic shell protein building block with an inverted sidedness of its N- and C-terminal residues relative to its natural counterpart; the inversion targets genetically fused protein cargo to the lumen of the shell. Moreover, the titer of fluorescent protein cargo encapsulated using this strategy is controllable using an inducible tetracycline promoter. These results expand the available set of building blocks for precision engineering of BMC-based nanoreactors and are compatible with orthogonal methods which will facilitate the installation and organization of multi-enzyme pathways.
•Circular permutation of a BMC shell protein redirects its termini toward the lumen.•The permuted shell protein forms hexamers and can assemble into intact shells.•Genetically fused cargo is targeted to the lumen of the shell.•By varying the induction level 10–80 cargo molecules can be encapsulated per shell.
Bacterial cells have long been thought to be simple cells with little spatial organization, but recent research has shown that they exhibit a remarkable degree of subcellular differentiation. Indeed, ...bacteria even have organelles such as magnetosomes for sensing magnetic fields or gas vesicles controlling cell buoyancy. A functionally diverse group of bacterial organelles are the bacterial microcompartments (BMCs) that fulfill specialized metabolic needs. Modification and reengineering of these BMCs enable innovative approaches for metabolic engineering and nanomedicine.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Bacterial microcompartments (BMCs) are organelles that segregate segments of metabolic pathways which are incompatible with surrounding metabolism. BMCs consist of a selectively permeable ...shell, composed of three types of structurally conserved proteins, together with sequestered enzymes that vary among functionally distinct BMCs. Genes encoding shell proteins are typically clustered with those for the encapsulated enzymes. Here, we report that the number of identifiable BMC loci has increased twenty-fold since the last comprehensive census of 2014, and the number of distinct BMC types has doubled. The new BMC types expand the range of compartmentalized catalysis and suggest that there is more BMC biochemistry yet to be discovered. Our comprehensive catalog of BMCs provides a framework for their identification, correlation with bacterial niche adaptation, experimental characterization, and development of BMC-based nanoarchitectures for biomedical and bioengineering applications.
This review focuses on the Orange Carotenoid Protein (OCP) which is the first photoactive protein identified containing a carotenoid as the photoresponsive chromophore. This protein is essential for ...the triggering of a photoprotective mechanism in cyanobacteria which decreases the excess absorbed energy arriving at the photosynthetic reaction centers by increasing thermal dissipation at the level of the phycobilisomes, the cyanobacterial antenna. Blue-green light causes structural changes within the carotenoid and the protein, converting the orange inactive form into a red active form. The activated red form interacts with the phycobilisome and induces the decrease of phycobilisome fluorescence emission and of the energy arriving to the photosynthetic reaction centers. The OCP is the light sensor, the signal propagator and the energy quencher. A second protein, the Fluorescence Recovery Protein (FRP), is needed to detach the red OCP from the phycobilisome and its reversion to the inactive orange form. In the last decade, in vivo and in vitro mechanistic studies combined with structural and genomic data resulted in both the discovery and a detailed picture of the function of the OCP and OCP-mediated photoprotection. Recent structural and functional results are emphasized and important previous results will be reviewed. Similarities to other blue-light responsive proteins will be discussed.
Dissociating the complexity of metabolic processes into modules is a shift in focus from the single gene/gene product to functional and evolutionary units spanning the scale of biological ...organization. When viewing the levels of biological organization through this conceptual lens, modules are found across the continuum: domains within proteins, co-regulated groups of functionally associated genes, operons, metabolic pathways and (sub)cellular compartments. Combining modules as components or subsystems of a larger system typically leads to increased complexity and the emergence of new functions. By virtue of their potential for ‘plug and play’ into new contexts, modules can be viewed as units of both evolution and engineering. Through consideration of lessons learned from recent efforts to install new metabolic modules into cells and the emerging understanding of the structure, function and assembly of protein-based organelles, bacterial microcompartments, a structural bioengineering approach is described: one that builds from an architectural vocabulary of protein domains. This bioarchitectonic approach to engineering cellular metabolism can be applied to microbial cell factories, used in the programming of members of synthetic microbial communities or used to attain additional levels of metabolic organization in eukaryotic cells for increasing primary productivity and as the foundation of a green economy.
This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.
We have discovered a new cluster of genes that is found exclusively in the Actinobacteria phylum. This locus includes genes for the 2-aminophenol
-cleavage pathway and the shell proteins of a ...bacterial microcompartment (BMC) and has been named aromatics (ARO) for its putative role in the breakdown of aromatic compounds. In this study, we provide details about the distribution and composition of the ARO BMC locus and conduct phylogenetic, structural, and functional analyses of the first two enzymes in the catabolic pathway: a unique 2-aminophenol dioxygenase, which is exclusively found alongside BMC shell genes in Actinobacteria, and a semialdehyde dehydrogenase, which works downstream of the dioxygenase. Genomic analysis reveals variations in the complexity of the ARO loci across different orders. Some loci are simple, containing shell proteins and enzymes for the initial steps of the catabolic pathway, while others are extensive, encompassing all the necessary genes for the complete breakdown of 2-aminophenol into pyruvate and acetyl-CoA. Furthermore, our analysis uncovers two subtypes of ARO BMC that likely degrade either 2-aminophenol or catechol, depending on the presence of a pathway-specific gene within the ARO locus. The precise precursor of 2-aminophenol, which serves as the initial substrate and/or inducer for the ARO pathway, remains unknown, as our model organism
cannot utilize 2-aminophenol as its sole energy source. However, using enzymatic assays, we demonstrate the dioxygenase's ability to cleave both 2-aminophenol and catechol
, in collaboration with the aldehyde dehydrogenase, to facilitate the rapid conversion of these unstable and toxic intermediates. IMPORTANCE Bacterial microcompartments (BMCs) are proteinaceous organelles that are widespread among bacteria and provide a competitive advantage in specific environmental niches. Studies have shown that the genetic information necessary to form functional BMCs is encoded in loci that contain genes encoding shell proteins and the enzymatic core. This allows the bioinformatic discovery of BMCs with novel functions and expands our understanding of the metabolic diversity of BMCs. ARO loci, found only in Actinobacteria, contain genes encoding for phylogenetically remote shell proteins and homologs of the
-cleavage degradation pathway enzymes that were shown to convert central aromatic intermediates into pyruvate and acetyl-CoA in gamma Proteobacteria. By analyzing the gene composition of ARO BMC loci and characterizing two core enzymes phylogenetically, structurally, and functionally, we provide an initial functional characterization of the ARO BMC, the most unusual BMC identified to date, distinctive among the repertoire of studied BMCs.
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