Recombinant Synechococcus elongatus Cobalamin synthase (cobS)
Description
Protein Identity and Basic Properties
Recombinant Synechococcus elongatus cobalamin synthase (cobS) is a protein derived from the cyanobacterium Synechococcus elongatus strain PCC 7942, also known as Anacystis nidulans R2. According to available product information, the protein is identified with the UniProt accession number Q8GMS2 and is encoded by the cobS gene (locus name: Synpcc7942_0454, ORF name: sek0016) . The full-length protein consists of 251 amino acids and is classified under EC number 2.-.-.- in the enzyme nomenclature system, indicating it belongs to the transferase class, though its specific subclass has not been fully determined .
Table 1. Molecular Characteristics of Recombinant Synechococcus elongatus Cobalamin Synthase
| Property | Description |
|---|---|
| Source Organism | Synechococcus elongatus (strain PCC 7942) |
| Alternative Name | Anacystis nidulans R2 |
| UniProt Accession | Q8GMS2 |
| Gene Name | cobS |
| Locus Name | Synpcc7942_0454 |
| ORF Name | sek0016 |
| Expression Region | 1-251 |
| Enzyme Classification | EC 2.-.-.- |
| Protein Length | 251 amino acids |
Cobalamin Biosynthesis Pathway
Cobalamin (vitamin B12) is a complex cobalt-containing tetrapyrrole that serves as an essential cofactor for numerous enzymes across various organisms. The biosynthesis of cobalamin involves a multistep pathway requiring approximately 30 enzymatic reactions. While specific details of the Synechococcus elongatus cobS catalytic mechanism are not extensively documented in available research, studies on homologous enzymes suggest it plays a crucial role in the later stages of cobalamin biosynthesis, particularly in the assembly of the nucleotide loop structure of the cobalamin molecule .
The importance of cobalamin in cyanobacterial metabolism is highlighted by studies on related Synechococcus strains. For instance, Synechococcus sp. strain PCC 7002 exhibits cobalamin auxotrophy, requiring exogenous cobalamin for growth . Research has demonstrated that in this organism, cobalamin is primarily needed for methionine biosynthesis through the function of the cobalamin-dependent methionine synthase (MetH) . The auxotrophy of PCC 7002 can be complemented by introducing the metE gene (encoding cobalamin-independent methionine synthase) from Synechococcus sp. strain PCC 73109, suggesting that methionine biosynthesis might be the sole function requiring cobalamin in some Synechococcus strains .
Relationship to Other Cobalamin-Processing Enzymes
While direct information on cobS interaction with other enzymes is limited, insights can be drawn from research on related cobalamin-processing enzymes. For example, studies on ATP:co(I)rrinoid adenosyltransferases (ACATs), which are involved in cobalamin activation, have revealed mechanistic details about how certain enzymes interact with cobalamin precursors . In particular, some of these enzymes can generate a transient four-coordinate cobalamin intermediate, which is critical for the formation of the adenosylcobalamin Co-C bond .
Table 2. Key Enzymes in Cobalamin Metabolism in Cyanobacteria
| Enzyme | Function | Relevance to cobS |
|---|---|---|
| Cobalamin Synthase (cobS) | Assembly of nucleotide loop in cobalamin structure | Central focus of this report |
| Methionine Synthase (MetH) | Cobalamin-dependent methionine biosynthesis | Major consumer of cobS product |
| Methionine Synthase (MetE) | Cobalamin-independent methionine biosynthesis | Alternative pathway in some species |
| ATP:co(I)rrinoid Adenosyltransferases | Formation of adenosylcobalamin | Processes cobalamin to active form |
| Cobalamin Riboswitch | Transcriptional regulation of cobalamin-related genes | May regulate cobS expression |
Expression and Purification
The production of recombinant Synechococcus elongatus cobS likely involves heterologous expression systems, though specific details of expression methods are not provided in available research. According to product information, the recombinant protein is expressed with a tag to facilitate purification, although the specific tag type is determined during the production process . For membrane proteins like cobS, expression often requires specialized systems that can properly fold and integrate such proteins.
The final preparation of recombinant cobS is stored in a Tris-based buffer containing 50% glycerol, optimized for maintaining protein stability . The high glycerol concentration helps prevent protein denaturation during freeze-thaw cycles and provides a stabilizing environment for the enzyme structure.
Metabolic Engineering Applications
Understanding and manipulating cobalamin biosynthesis in cyanobacteria has significant biotechnological implications. Cyanobacteria like Synechococcus are increasingly recognized as promising platforms for sustainable biotechnology, capable of converting solar energy and carbon dioxide into valuable compounds . The strain Synechococcus sp. PCC 11901, for example, has been reported to have a short doubling time of approximately 2 hours, to grow at high light intensities and in a wide range of salinities, and to accumulate up to 33 g dry cell weight per liter when cultured under optimized conditions .
Recombinant cobS could potentially be used in metabolic engineering approaches to enhance cobalamin production in cyanobacteria or to introduce the pathway into other organisms. Given that vitamin B12 is an essential nutrient for many organisms, including humans, strains engineered for improved cobalamin synthesis could have applications in nutritional supplements or fortified foods.
Tools for Genetic Manipulation
Recent advances in genetic tools for Synechococcus, including methods for markerless strain development, provide promising approaches for investigating and potentially enhancing cobS function in vivo. For instance, a method has been developed using a mutated phenylalanyl-tRNA synthetase gene (pheS) for counter-selection in Synechococcus sp. PCC 7002, offering a way to create precise genomic modifications without leaving antibiotic resistance markers .
Such genetic tools could be valuable for creating strains with altered cobS expression or activity, or for introducing mutations to study structure-function relationships in a native context. These approaches might help elucidate the role of cobS in cobalamin biosynthesis and potentially lead to strains with enhanced cobalamin production capabilities.
Table 4. Potential Applications of Recombinant cobS Research
| Application Area | Specific Uses | Relevant Context |
|---|---|---|
| Structural Biology | Determination of three-dimensional structure | Contribution to enzyme mechanism understanding |
| Enzyme Kinetics | Characterization of catalytic parameters | Insights into reaction mechanism |
| Metabolic Engineering | Enhancement of cobalamin production | Nutritional applications, sustainable production |
| Synthetic Biology | Reconstruction of cobalamin pathway | Transfer to heterologous hosts |
| Stress Response Studies | Investigation of role in stress adaptation | Connection to findings in related strains |
Cobalamin Metabolism in Different Synechococcus Strains
Different Synechococcus strains exhibit varying requirements for cobalamin, which may reflect differences in their metabolic capabilities and environmental adaptations. As mentioned earlier, Synechococcus sp. strain PCC 7002 is cobalamin auxotrophic, primarily requiring this cofactor for methionine biosynthesis . In contrast, Synechococcus sp. strain PCC 73109 possesses genes for both cobalamin-dependent (MetH) and cobalamin-independent (MetE) methionine synthases, making it non-auxotrophic for cobalamin .
The presence of a cobalamin riboswitch in the promoter region of metE from Synechococcus sp. strain PCC 73109 has been reported to act as a cobalamin-dependent transcriptional attenuator for metE expression . This regulatory mechanism allows the organism to respond to cobalamin availability by modulating the expression of the cobalamin-independent pathway accordingly.
Stress Response and Metabolic Adaptations
Research on related Synechococcus strains provides insights into potential connections between cobalamin metabolism and stress responses. For instance, studies on Synechococcus elongatus PCC 7942 have shown that mutants defective in glycogen synthesis enzymes (ADP-glucose pyrophosphorylase and glycogen synthase) exhibit decreased photosynthetic oxygen evolution and respiration rates, as well as increased sensitivity to salt and oxidative stress . While this does not directly involve cobS, it illustrates how disruptions in metabolic pathways can affect stress tolerance in cyanobacteria.
In another example, a single amino acid substitution (C252Y) in the F₀F₁ ATP synthase subunit α (AtpA) has been identified as a primary contributor to improved stress tolerance in Synechococcus elongatus UTEX 2973 compared to PCC 7942, despite their genomes being 99.8% identical . Such findings highlight the potential significance of specific enzymes and metabolic pathways in determining stress tolerance and adaptability in Synechococcus species.
Table 5. Comparison of Cobalamin Requirements and Related Features in Synechococcus Strains
| Synechococcus Strain | Cobalamin Requirement | MetE/MetH Status | Notable Features |
|---|---|---|---|
| PCC 7002 | Auxotrophic | MetH only | Requires cobalamin for methionine synthesis |
| PCC 73109 | Non-auxotrophic | Both MetE and MetH | Contains cobalamin riboswitch controlling metE |
| PCC 7942 | Not specified in available literature | Not specified | Host of the cobS gene studied here |
| PCC 11901 | Not specified in available literature | Not specified | Fast growth, high biomass accumulation potential |
Future Research Opportunities
Several promising directions for future research on Synechococcus elongatus cobS include:
-
Detailed structural analysis through X-ray crystallography, cryo-electron microscopy, or other structural determination methods to elucidate the three-dimensional configuration of the enzyme.
-
Biochemical characterization to determine substrate specificity, catalytic parameters, and potential cofactor requirements, leading to a better understanding of the enzyme's mechanism.
-
Investigation of regulatory mechanisms controlling cobS expression in response to environmental conditions, potentially including the identification of any riboswitches or other regulatory elements.
-
Metabolic engineering approaches to enhance cobalamin production in cyanobacteria or to introduce the pathway into other organisms, with potential applications in biotechnology and nutrition.
-
Exploration of the potential role of cobS in stress response and environmental adaptation, similar to findings for other metabolic enzymes in Synechococcus strains.
Table 6. Key Research Questions for Future Investigation
| Research Area | Specific Questions | Potential Approaches |
|---|---|---|
| Structure | What is the three-dimensional structure of cobS? | X-ray crystallography, cryo-EM, computational modeling |
| Mechanism | What are the substrates and catalytic mechanism? | Enzymatic assays, site-directed mutagenesis |
| Regulation | How is cobS expression regulated? | Transcriptomics, promoter analysis, riboswitch identification |
| Engineering | Can cobS activity be enhanced for improved cobalamin production? | Protein engineering, directed evolution |
| Systems Biology | How does cobS interact with other enzymes in the pathway? | Protein-protein interaction studies, metabolomics |
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you have a specific format preference, please indicate it in your order remarks, and we will accommodate your request.
Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please inform us in advance, as additional fees will apply.
Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. The shelf life of lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: syf:Synpcc7942_0454
STRING: 1140.Synpcc7942_0454
Q&A
What is Synechococcus elongatus Cobalamin synthase (cobS)?
Cobalamin synthase (cobS) is an essential enzyme in the biosynthetic pathway of cobalamin (vitamin B12) in Synechococcus elongatus. This protein is formally designated with EC number 2.-.-.- and has been identified in multiple strains including S. elongatus PCC 7942. The protein consists of 251 amino acids and functions in the complex multi-step pathway of cobalamin synthesis, contributing to one of nature's most structurally complex small molecules requiring approximately 30 enzyme-mediated steps for complete synthesis . The cobS protein catalyzes crucial reactions in the later stages of cobalamin biosynthesis, specifically in the assembly of the corrin ring structure.
What genomic information is available for cobS in Synechococcus elongatus?
The cobS gene has been well-characterized in Synechococcus elongatus PCC 7942. According to sequence databases, the gene is annotated as Synpcc7942_0454 (also known by the ORF name sek0016) . Genomic sequencing and comparative genomics have facilitated the identification of this gene across multiple cyanobacterial strains. The Synechococcus elongatus genome has been extensively mapped, with PCC 7942 serving as a model organism, while newer strains like PCC 11801 and PCC 11802 share significant genomic identity (approximately 83% and 97% respectively with PCC 7942), suggesting similar cobS functionality with potential strain-specific variations .
What expression systems are most effective for producing recombinant cobS?
-
E. coli-based systems: When expressing cobS in E. coli, researchers should be aware that the full-length protein may remain inside the cells due to poor recognition of its signal peptide by the bacterial Tat (twin-arginine translocation) export machinery . This can significantly impact purification strategies.
-
Cyanobacterial expression: For expression within cyanobacteria, the trc promoter has been demonstrated to ensure constitutive protein production regardless of growth conditions. Transformation vectors like pAM1303 can facilitate double homologous recombination of cloned DNA fragments into neutral regions of the Synechococcus genome .
-
Signal peptide optimization: Researchers should consider using alternative signal peptides, such as LTorA (from Escherichia coli TorA protein) or LCya (from Cyanothece sp. ATCC 51142), which have proven effective for the periplasmic expression of similar proteins .
What are the optimal conditions for storing and handling recombinant cobS?
Based on experimental data, the following storage and handling conditions are recommended for maintaining recombinant cobS stability and activity:
-
Short-term storage: Store working aliquots at 4°C for up to one week to minimize freeze-thaw cycles while maintaining activity.
-
Long-term storage: Store at -20°C, or for extended storage, conserve at -20°C or -80°C in storage buffer containing Tris-based buffer with 50% glycerol optimized for protein stability.
-
Handling considerations: Repeated freezing and thawing is not recommended as it may lead to protein denaturation and loss of enzymatic activity .
-
Buffer conditions: When working with cobS, researchers should avoid reducing agents such as dithiothreitol in isolation buffers, as evidence suggests that cobS contains essential disulfide bonds that enable redox control of its activity .
What methods are used to assess cobS enzymatic activity?
Assessment of cobS enzymatic activity requires specialized approaches due to its role in the complex cobalamin biosynthetic pathway:
-
Spectrophotometric assays: Activity can be monitored by following the conversion of pathway intermediates using UV-visible spectroscopy, tracking characteristic absorption changes associated with corrin ring modifications.
-
Coupled enzyme assays: Due to cobS's position in a multi-step pathway, coupled assays that monitor the production of downstream metabolites or consumption of substrates can provide indirect measurements of activity.
-
Mass spectrometry: LC-MS/MS approaches allow detailed characterization of reaction intermediates and products, offering insights into the catalytic mechanism.
-
In vivo complementation: Functional activity can be assessed through complementation studies in cobS-deficient strains, evaluating the restoration of cobalamin biosynthesis pathways.
How does cobS function differ across Synechococcus elongatus strains?
Different Synechococcus elongatus strains exhibit variations in metabolic capabilities and gene expression patterns that may influence cobS function:
-
Strain-specific differences: While closely related, S. elongatus strains like PCC 7942, PCC 11801, and PCC 11802 show metabolic variations that may affect cobS activity and regulation. For instance, PCC 11802 exhibits higher levels of key intermediate metabolites compared to PCC 11801, suggesting it might be better suited for achieving high metabolic flux in engineered pathways .
-
Genomic variations: Despite high genome identity between strains (e.g., 97% between PCC 11801 and PCC 11802), single nucleotide polymorphisms (SNPs) in genes like atpA, ppnK, and rpaA have been identified as responsible for differences in growth rates and environmental stress tolerance, which could indirectly influence cobS expression and activity .
-
Carbon metabolism connection: The regulation of carbon metabolism genes differs between strains, with PCC 11802 showing less repression of Calvin cycle enzymes under elevated CO2 conditions compared to PCC 11801. This difference in central carbon metabolism may impact the supply of precursors for cobalamin synthesis .
How can cobS be incorporated into metabolic engineering strategies?
Cobalamin synthase has potential applications in metabolic engineering for enhanced production of vitamin B12 and related compounds:
-
Pathway optimization: Expression of cobS alongside other cobalamin biosynthesis genes can establish a complete B12 production pathway in recombinant hosts. Careful balancing of enzyme expression levels is critical for optimal pathway flux.
-
Integration with carbon fixation enhancement: Strategies that focus on improving carbon fixation rates through the Calvin-Benson-Bassham (CBB) cycle could provide more precursors for cobalamin synthesis. Research has demonstrated that overexpression of key CBB enzymes (RuBisCO, Sedoheptulose bisphosphatase, fructose bisphosphate aldolase, or transketolase) can improve total carbon fixation rates and enhance heterologous production of target compounds .
-
Riboswitch-based regulation: Implementation of native or synthetic riboswitches, such as the theophylline-dependent riboswitch demonstrated in S. elongatus PCC 7942, allows strict regulation of gene expression. A native cobalamin-dependent riboswitch has been reported in Synechococcus PCC 7002, which could potentially be utilized for feedback regulation of cobS expression .
What is the relationship between cobS and CO2-concentrating mechanisms in Synechococcus elongatus?
Recent research has revealed interesting connections between cobalamin biosynthesis and CO2-concentrating mechanisms (CCM) in Synechococcus elongatus:
-
CCM gene expression patterns: Studies on S. elongatus PCC 7942 have documented expression patterns of CCM-associated genes during adaptation to different carbon dioxide conditions, including the replacement of CO2 with HCO3- and exposure to extremely high CO2 levels (up to 100%) .
-
NDH-1 system regulation: Increases in CO2 concentration coincide with the suppression of the NDH-14 system, which was previously thought to function constitutively. This finding reveals previously unknown regulatory mechanisms that may indirectly affect cobalamin synthesis .
-
Carbonic anhydrase interactions: The presence of periplasmic carbonic anhydrases (CAs) like EcaA in Synechococcus elongatus affects carbon acquisition and utilization. Experimental evidence suggests mechanisms that limit the appearance of native EcaA (EcaA Syn) in the periplasm under standard laboratory conditions, which could influence the cellular environment in which cobS functions .
What strategies can be used to enhance cobS expression and activity?
Several approaches have been developed to optimize cobS expression and activity for research and biotechnological applications:
How can researchers effectively analyze cobS-substrate interactions?
Understanding the interactions between cobS and its substrates requires specialized analytical techniques:
-
Isothermal titration calorimetry (ITC): This method provides direct measurements of binding thermodynamics between cobS and its substrates or cofactors.
-
Surface plasmon resonance (SPR): SPR allows real-time monitoring of binding kinetics and affinity between cobS and its interaction partners.
-
X-ray crystallography: Determination of cobS structure in complex with substrates or substrate analogs can provide atomic-level insights into the catalytic mechanism.
-
Hydrogen-deuterium exchange mass spectrometry (HDX-MS): This technique can identify regions of cobS that undergo conformational changes upon substrate binding, providing structural insights even in the absence of crystal structures.
What are the emerging techniques for studying cobS function in situ?
Emerging technologies are expanding our ability to study cobS function within its native cellular context:
-
CRISPR-Cas9 genome editing: Precise modification of the cobS gene or its regulatory elements in Synechococcus elongatus enables detailed structure-function analyses and investigation of regulatory mechanisms.
-
Single-cell analyses: Techniques such as single-cell RNA-seq and microfluidics approaches allow investigation of cell-to-cell variability in cobS expression and function.
-
Metabolic flux analysis: Isotope labeling combined with metabolomics enables tracking of carbon flow through the cobalamin biosynthetic pathway, revealing rate-limiting steps and regulatory nodes.
-
Proximity labeling proteomics: Methods like BioID or APEX2 can identify proteins that interact with cobS in vivo, providing insights into the composition of multienzyme complexes involved in cobalamin biosynthesis.
How might cobS research contribute to biofuel production studies?
Research on cobS has potential implications for biofuel production systems, particularly those utilizing cyanobacteria:
-
Integration with biofuel pathways: Understanding and optimizing cobS function could contribute to engineering efforts for producing biofuel feedstocks. The COBS (Comparison of Biofuels Systems) experiments already seek to identify and develop cropping systems for biofuel feedstock production while improving biodiversity and protecting soil and water resources .
-
Carbon fixation enhancement: As cobalamin is involved in various metabolic processes, optimizing cobS and related enzymes could indirectly enhance carbon fixation efficiency. Improved carbon fixation has been shown to increase the production of biofuels and other valuable compounds in cyanobacteria .
-
Strain selection considerations: The choice of Synechococcus elongatus strain (e.g., PCC 7942, PCC 11801, or PCC 11802) for metabolic engineering should consider the distinct metabolic capabilities of each strain. For instance, PCC 11802 has been identified as potentially better suited for achieving high metabolic flux in engineered pathways due to its higher levels of key intermediate metabolites .
