Recombinant Clostridium acetobutylicum DNA translocase FtsK (ftsK)

What is the primary function of FtsK in Clostridium acetobutylicum?

FtsK in C. acetobutylicum, similar to its homologs in other bacteria, functions as a DNA translocase that coordinates cell division with chromosome segregation. It plays a critical role in ensuring proper distribution of genetic material during cellular division processes. FtsK is particularly important during septation, where it helps resolve chromosome dimers and ensures complete chromosome segregation before cell division is completed .

How is the ftsK gene organized in the C. acetobutylicum genome?

The ftsK gene is part of the 3.94-Mb chromosome of C. acetobutylicum ATCC 824. Based on comparative genomic analyses with other Clostridial species, the gene is likely located in a conserved region of the chromosome rather than on the 192-kb megaplasmid pSOL1 that contains genes mainly responsible for solvent production. The complete genome sequence of C. acetobutylicum has been determined using the shotgun approach, which provides the basis for identifying and characterizing genes like ftsK .

How does FtsK in C. acetobutylicum compare to its homologs in other bacterial species?

While specific comparative studies of C. acetobutylicum FtsK with other species aren't directly presented in the search results, we can infer that there are functional similarities with FtsK proteins in other bacteria. For instance, in Clostridioides difficile, FtsK is phosphorylated under the control of PrkC and is involved in coordinating cell division with chromosome segregation . FtsK likely shares functional similarities with DNA translocases like SpoIIIE in Bacillus subtilis, which is involved in DNA translocation during sporulation . Comparative analysis between C. acetobutylicum and B. subtilis genomes reveals significant local conservation of gene order, suggesting potential conservation of FtsK function despite species differences .

What are the most effective methods for cloning the ftsK gene from C. acetobutylicum?

For cloning the ftsK gene from C. acetobutylicum, a PCR-based approach using specific primers designed from the genome sequence is most effective. Based on methodologies used for similar proteins, the following protocol is recommended:

• Design primers based on the published C. acetobutylicum genome sequence, including appropriate restriction sites for subsequent cloning.

• Amplify the complete gene by PCR using high-fidelity polymerase.

• Clone the amplified fragment into an appropriate vector, such as a modified pDIA6103 vector system, which has been successfully used for cloning genes in Clostridial species .

For optimal results, consider using Gibson Assembly for seamless cloning, particularly when creating translational fusions, as demonstrated with FtsK-SNAP fusions in related organisms .

What expression systems are most suitable for producing recombinant C. acetobutylicum FtsK?

Based on successful approaches with Clostridial proteins, the following expression systems are recommended:

• Inducible expression in E. coli: Using vectors with T7 or similar strong promoters for initial characterization studies.

• Native expression in C. acetobutylicum: Using an ATc-inducible Ptet promoter system for expressing FtsK in its native environment .

• Controlled expression using the Ptet inducible promoter: This has been successfully used for FtsK expression in Clostridioides difficile and could be adapted for C. acetobutylicum .

When expressing full-length FtsK, it's important to consider that membrane-associated proteins may require specific solubilization strategies or expression of truncated functional domains.

What strategies are effective for purifying recombinant FtsK protein while maintaining its functional integrity?

Purification of functional FtsK requires careful consideration of its membrane association and large size. Based on successful approaches with similar proteins:

• Affinity tag selection: C-terminal His6 or HA tags have been successfully used with FtsK in related organisms without significantly affecting function .

• Solubilization conditions: Mild detergents (0.5-1% DDM or CHAPS) are typically needed to maintain the native conformation of membrane-associated regions.

• Truncated constructs: Consider purifying the C-terminal motor domain separately if full-length protein purification proves challenging.

• On-column refolding: This can be effective if the protein forms inclusion bodies during expression.

For activity studies, it's crucial to verify that purified FtsK retains ATP hydrolysis capability, as this is essential for its translocase function.

How does phosphorylation regulate FtsK activity in Clostridium species?

Phosphorylation plays a significant role in regulating FtsK activity in Clostridial species. In Clostridioides difficile, FtsK is phosphorylated in vivo under the control of the serine/threonine kinase PrkC . This phosphorylation likely regulates FtsK's role in coordinating cell division with chromosome segregation.

Specifically, the data indicates that threonine residues are enriched among phosphopeptides more phosphorylated in Δstp mutants (where STP is a serine/threonine phosphatase), suggesting a phosphorylation-dephosphorylation cycle controls FtsK activity . This post-translational modification may serve as a regulatory mechanism that ensures proper timing of DNA segregation relative to cell division.

What methods are most effective for identifying phosphorylation sites on recombinant FtsK?

Based on successful approaches with FtsK in related organisms, the following methods are recommended for identifying phosphorylation sites:

• Mass spectrometry-based phosphoproteomics: This approach has successfully identified phosphorylation sites in Clostridial proteins, including FtsK. Comparative phosphoproteome analysis between wild-type and kinase-deficient mutants (ΔprkC) can help identify kinase-specific phosphorylation sites .

• Site-directed mutagenesis: After identifying potential phosphorylation sites by mass spectrometry, site-directed mutagenesis can be used to replace specific threonine or serine residues with alanine (mimicking non-phosphorylation) or glutamate (mimicking constitutive phosphorylation). For example, mutagenesis of T318 to alanine has been performed in FtsK studies to investigate the functional significance of phosphorylation .

• In vitro kinase assays: Using purified PrkC kinase with recombinant FtsK can confirm direct phosphorylation and help identify specific phosphorylation sites.

What is the functional significance of threonine phosphorylation at position 318 on FtsK?

Threonine 318 (T318) has been identified as a significant phosphorylation site on FtsK in Clostridial species. Site-directed mutagenesis studies where T318 was replaced with alanine (to mimic non-phosphorylation) have provided insights into its functional significance .

The phosphorylation state of T318 likely affects:

• FtsK's interaction with DNA during chromosome segregation

• Its ATPase activity, which is essential for DNA translocation

• Proper timing of DNA segregation relative to cell division

• Potential protein-protein interactions with other divisome components

While specific details about phenotypic changes resulting from T318A mutation in C. acetobutylicum FtsK are not directly presented in the search results, research on related organisms suggests that this phosphorylation site is critical for coordinating cell division with chromosome segregation, particularly under stress conditions or during sporulation .

What in vitro assays can be used to measure the DNA translocase activity of recombinant FtsK?

Several in vitro assays can be employed to measure the DNA translocase activity of recombinant FtsK:

• ATP hydrolysis assays: Measuring ATPase activity in the presence of DNA substrates using colorimetric phosphate detection methods or coupled enzyme assays with NADH oxidation.

• DNA translocation assays: Using fluorescently labeled DNA substrates and monitoring their displacement in real-time through FRET-based approaches or single-molecule techniques.

• Triplex displacement assays: These assays use a triplex-forming oligonucleotide bound to a specific site on a DNA substrate. As FtsK translocates along the DNA, it displaces the triplex, which can be measured by changes in fluorescence.

• Magnetic tweezers assays: These allow direct observation of FtsK-mediated DNA translocation at the single-molecule level by measuring changes in DNA length during translocation.

The selection of appropriate DNA substrates is crucial, particularly those containing FtsK-recognition sequences or dif-like sites that would be recognized by the C. acetobutylicum FtsK.

How can the interaction between FtsK and the bacterial genome be studied in vivo?

Several approaches can be used to study FtsK-genome interactions in vivo:

• Fluorescent protein fusions: Creating FtsK-SNAP or FtsK-GFP fusions allows visualization of FtsK localization during cell division and sporulation. This approach has been successfully used with FtsK and can be adapted for C. acetobutylicum .

• Chromatin immunoprecipitation (ChIP): Using HA-tagged FtsK constructs for ChIP analysis to identify DNA binding sites throughout the genome. This approach has been used with FtsK-HA tagged proteins in Clostridial species .

• Inducible antisense RNA systems: Depleting FtsK using antisense RNA expression systems allows examination of chromosome segregation defects. This approach has been used with FtsK in Clostridioides difficile and could be adapted for C. acetobutylicum .

• Time-lapse microscopy: Combined with fluorescently labeled chromosomal loci, this can reveal the dynamics of FtsK-mediated chromosome segregation during cell division or sporulation.

What approaches can detect FtsK-dependent chromosome segregation during sporulation in C. acetobutylicum?

To detect FtsK-dependent chromosome segregation during sporulation in C. acetobutylicum, researchers can employ several sophisticated approaches:

• Cre-loxP recombination assay: This system can determine if plasmid or chromosomal DNA enters the forespore before or after septation. By placing a Cre-dependent reporter (PFS-loxP-kan-loxP-gfp) near the chromosomal terminus and expressing Cre recombinase in either the mother cell or forespore compartment, researchers can track DNA translocation during sporulation .

• Fluorescence microscopy with DNA dyes: Using membrane and DNA dyes in combination with time-lapse microscopy to visualize chromosome translocation during sporulation.

• FtsK depletion or mutation studies: Creating conditional FtsK mutants or depletions using inducible antisense RNA systems to assess the impact on chromosome segregation during sporulation .

• Spore inheritance assays: Measuring the efficiency of plasmid or chromosomal marker inheritance in spores in wild-type versus FtsK-mutant strains can reveal FtsK's role in DNA segregation during sporulation .

The data from studies in other species suggest that DNA segregation during sporulation occurs before septation and can be independent of certain DNA translocases, though FtsK may still play important roles in ensuring complete chromosome capture in the forespore .

How does the ATPase activity of FtsK coordinate with its DNA binding function during chromosome segregation?

The coordination between ATPase activity and DNA binding function of FtsK involves a sophisticated mechanism:

• Sequential activation: The N-terminal domain of FtsK typically anchors to the division septum, while the C-terminal motor domain binds specific DNA sequences (FtsK-orienting polar sequences or KOPS). Upon DNA binding, conformational changes activate the ATPase domain.

• Directional translocation: ATP hydrolysis powers directional movement of FtsK along DNA. This directionality is crucial for proper segregation of the terminus region of bacterial chromosomes.

• DNA sequence recognition: The γ-subdomain of FtsK likely recognizes specific DNA sequences that guide its loading and orientation on the chromosome, ensuring that translocation occurs in the correct direction toward the dif site.

• Coupling to recombination: In many bacteria, FtsK activates XerCD recombinases at the dif site to resolve chromosome dimers, a process that requires both DNA binding and ATP hydrolysis.

While the search results don't provide specific details on C. acetobutylicum FtsK's ATPase activity, research on related DNA translocases like AlfA shows that dynamic assembly correlates with segregation function, suggesting similar principles may apply to FtsK .

What is the relationship between FtsK activity and the phosphorylation state of other cell division proteins?

The relationship between FtsK activity and the phosphorylation state of other cell division proteins represents a complex regulatory network:

• Coordinated phosphorylation: In Clostridioides difficile, both FtsK and other cell division proteins are targets of the serine/threonine kinase PrkC. This suggests a coordinated phosphorylation cascade regulates multiple components of the cell division machinery .

• Pathway integration: Phosphoproteome analysis identified 114 proteins phosphorylated under PrkC control, suggesting FtsK functions within a broader phosphorylation-regulated network. These pathways include metabolism, translation, stress response, cell division, and peptidoglycan metabolism .

• Divisome assembly timing: Phosphorylation may control the timing of FtsK recruitment relative to other divisome components, ensuring chromosome segregation is coordinated with septum formation.

• Cross-regulation: The phosphorylation state of FtsK may influence its interactions with other divisome components, and conversely, the phosphorylation state of other proteins may regulate FtsK activity.

The identification of WhiA (a sporulation-associated transcription factor) as another PrkC target suggests potential coordination between chromosome segregation and the initiation of sporulation programs .

How do protein-protein interactions influence FtsK function during different growth phases?

FtsK function is modulated by various protein-protein interactions that change during different growth phases:

• Vegetative growth interactions: During normal growth, FtsK likely interacts with:

  • Core divisome components (FtsZ, FtsA, FtsQ)

  • DNA repair and recombination proteins

  • Chromosome-associated proteins that help position the DNA at the division site

• Sporulation-specific interactions: During sporulation, a different set of interactions becomes important:

  • RacA, which anchors the chromosome to the cell pole during sporulation, appears to contribute to plasmid segregation along with AlfA (a plasmid-encoded actin-like protein) in B. subtilis . Similar mechanisms might exist for chromosome segregation involving FtsK in C. acetobutylicum.

  • Spo0A, a master regulator of sporulation that is phosphorylated by PrkC in vitro, may indirectly influence FtsK function during sporulation .

• Stress response interactions: Under stress conditions, FtsK may interact with:

  • Proteins involved in the SOS response

  • Stress-specific divisome components

  • Alternative DNA repair pathways

The search results indicate that in C. difficile, both FtsK and Spo0A are substrates of PrkC, suggesting potential coordination between cell division and sporulation initiation through phosphorylation-dependent interactions .

What are the most effective approaches for creating site-directed mutations in C. acetobutylicum ftsK?

Based on techniques successfully applied to Clostridial species, the following approaches are recommended for creating site-directed mutations in C. acetobutylicum ftsK:

• Plasmid-based mutagenesis followed by conjugation:

  • Perform site-directed mutagenesis on ftsK cloned into an E. coli plasmid (e.g., pDIA6103)

  • Transfer the mutated plasmid into C. acetobutylicum by conjugation

  • This approach has been successfully used to create the FtsK T318A mutation in related Clostridial species

• Inverse PCR method:

  • Amplify the entire plasmid containing ftsK using primers that introduce the desired mutation

  • Digest with DpnI to remove the template plasmid

  • Phosphorylate the PCR product with T4 polynucleotide kinase

  • Ligate using T4 ligase to recircularize the plasmid

• Gibson Assembly for complex modifications:

  • When creating fusion proteins or multiple modifications, Gibson Assembly provides seamless cloning

  • This method has been used successfully for creating FtsK-SNAP fusions

These genetic manipulation techniques have been validated in Clostridial species and can be adapted specifically for C. acetobutylicum.

What strategies can be used to create conditional ftsK mutants in C. acetobutylicum?

Creating conditional ftsK mutants in C. acetobutylicum requires approaches that allow controlled expression or inactivation:

• Inducible antisense RNA system:

  • Clone a fragment of ftsK (typically including the 5' UTR and beginning of the coding sequence, -40 to +140 relative to the start site) in antisense orientation

  • Place under control of an inducible promoter like Ptet

  • Transfer into C. acetobutylicum by conjugation

  • Induction leads to depletion of FtsK protein

• Inducible expression of wild-type or mutant ftsK:

  • Clone ftsK under control of an inducible promoter (e.g., Ptet)

  • Express in an ftsK-depleted background

  • This allows expression of mutant versions to assess their functionality

• Temperature-sensitive alleles:

  • Create random or directed mutations that produce temperature-sensitive protein variants

  • Screen for growth at permissive temperature and division defects at restrictive temperature

• Degron-based systems:

  • Fuse ftsK to inducible degron tags that target the protein for degradation when activated

  • This allows rapid and controlled depletion of the protein

The antisense RNA approach has been demonstrated to be effective in Clostridial species and represents a practical method for creating conditional ftsK mutants in C. acetobutylicum .

How can CRISPR-Cas9 systems be optimized for editing the ftsK gene in C. acetobutylicum?

Optimizing CRISPR-Cas9 systems for editing the ftsK gene in C. acetobutylicum requires addressing several specific challenges:

• Delivery system optimization:

  • Use vectors compatible with conjugative transfer into C. acetobutylicum

  • Consider using inducible promoters to control Cas9 expression

  • Design vectors with appropriate replication origins for Clostridium

• sgRNA design considerations:

  • Target unique sequences in ftsK to avoid off-target effects

  • Consider GC content and secondary structure of sgRNAs

  • Use bioinformatic tools specifically validated for Clostridial genomes

  • Design multiple sgRNAs targeting the same region to improve efficiency

• Homology-directed repair template design:

  • Include homology arms of at least 500-1000 bp for efficient recombination

  • Introduce silent mutations in the PAM sequence or seed region to prevent re-cutting

  • Consider using selection markers flanked by FRT sites for subsequent removal

• Screening and selection strategy:

  • Design PCR screening strategies to identify successful editing events

  • Consider using counterselection markers to enrich for edited cells

  • Use sequencing to confirm precise editing

While CRISPR-Cas9 editing in C. acetobutylicum was not directly addressed in the search results, genetic manipulation methods have been developed for this organism , and CRISPR systems have been adapted for other Clostridial species, providing a foundation for developing optimized protocols for ftsK editing.

How does FtsK function differ during vegetative growth versus sporulation in C. acetobutylicum?

FtsK likely exhibits distinct functional profiles during different growth phases in C. acetobutylicum:

During vegetative growth:

• Functions primarily in chromosome dimer resolution and segregation during normal cell division

• Works in conjunction with the standard cell division machinery

• May be regulated by phosphorylation via PrkC to coordinate with cell division timing

• Ensures complete chromosome segregation prior to septum closure

During sporulation:

• Takes on specialized roles related to asymmetric division and forespore chromosome translocation

• May function differently in the forespore versus the mother cell compartment

• Works in coordination with sporulation-specific proteins

In Bacillus subtilis, plasmid segregation during sporulation occurs before septation and independently of certain DNA translocases . If similar mechanisms exist in C. acetobutylicum, FtsK may play distinct roles during sporulation compared to vegetative growth. The phosphorylation of FtsK by PrkC, which also phosphorylates the sporulation master regulator Spo0A, suggests regulatory connections between cell division, chromosome segregation, and sporulation initiation .

What molecular mechanisms coordinate FtsK activity with the sporulation process?

Several molecular mechanisms likely coordinate FtsK activity with the sporulation process:

• Phosphorylation cascades: The serine/threonine kinase PrkC phosphorylates both FtsK and Spo0A (a master regulator of sporulation) . This suggests a coordinated phosphorylation mechanism that links chromosome segregation with sporulation initiation.

• Compartment-specific regulation: During sporulation, the cell divides asymmetrically, creating distinct mother cell and forespore compartments. FtsK activity may be regulated differently in each compartment.

• Interaction with sporulation-specific proteins: FtsK likely interacts with sporulation-specific chromosome organization proteins. In B. subtilis, RacA contributes to plasmid segregation during sporulation , suggesting similar mechanisms might exist for chromosome segregation involving FtsK in C. acetobutylicum.

• Altered substrate specificity: The DNA substrate recognized by FtsK may change during sporulation, possibly due to changes in DNA topology or chromosome organization.

• Temporal regulation: The timing of FtsK activity relative to other sporulation events is likely tightly controlled to ensure proper chromosome capture in the forespore.

These mechanisms ensure proper chromosome dynamics during the complex process of sporulation in C. acetobutylicum.

How does the expression and localization of FtsK change under different stress conditions?

Under different stress conditions, FtsK expression and localization likely undergo significant changes:

• Nutrient limitation response:

  • Increased expression or altered regulation of FtsK may occur as cells prepare for sporulation

  • Changes in FtsK phosphorylation state may alter its activity or localization

• Oxidative stress:

  • Phosphoproteome analysis shows that PrkC, which phosphorylates FtsK, also controls phosphorylation of proteins involved in stress responses

  • FtsK may relocalize to protect DNA or repair oxidative damage

• Temperature stress:

  • Heat or cold shock may alter FtsK expression or activity to ensure proper chromosome segregation under suboptimal conditions

  • Temperature-dependent changes in membrane fluidity may affect the membrane-anchored N-terminal domain of FtsK

• Solvent stress in C. acetobutylicum:

  • C. acetobutylicum is known for solvent production (acetone, butanol)

  • Solvent stress may trigger specific changes in FtsK activity to maintain genome integrity

• Cell wall stress:

  • PrkC controls phosphorylation of proteins involved in peptidoglycan metabolism

  • FtsK may interact differently with the divisome under cell wall stress conditions

These stress-responsive changes in FtsK expression and localization likely help maintain genome stability under adverse conditions, particularly when normal cell division processes are challenged.

What structural and functional differences exist between FtsK proteins in C. acetobutylicum and other Clostridial species?

Comparative analysis reveals several key differences between FtsK proteins across Clostridial species:

Structural differences:

• Domain organization may vary, particularly in the linker regions connecting the N-terminal membrane domain to the C-terminal motor domain

• The γ-subdomain, responsible for species-specific DNA recognition, likely shows the greatest sequence divergence

• Location and number of phosphorylation sites differ between species, affecting regulation

Functional differences:

• DNA sequence specificity: The recognition sequences (similar to KOPS in E. coli) likely vary between species, reflecting different chromosome organization

• Regulatory mechanisms: While phosphorylation by PrkC appears conserved in C. difficile , the specific regulatory pathways may differ in C. acetobutylicum

• Protein-protein interactions: The interacting partners of FtsK may vary between species, reflecting differences in cell division and sporulation machinery

Comparative genome analysis reveals significant local conservation of gene order between C. acetobutylicum and B. subtilis , suggesting that core functions of FtsK may be conserved while species-specific adaptations exist to accommodate differences in lifestyle and genome organization.

How can phylogenetic analysis inform experimental approaches to studying C. acetobutylicum FtsK?

Phylogenetic analysis provides valuable insights that can guide experimental approaches:

• Identifying conserved domains: Phylogenetic analysis can reveal highly conserved domains across Clostridial FtsK proteins, which likely represent functionally critical regions. These domains should be prioritized for structure-function studies and mutagenesis.

• Selecting heterologous expression systems: Understanding the evolutionary relationships between Clostridial species can help select the most appropriate heterologous expression systems for recombinant FtsK production.

• Guiding mutagenesis strategies: Comparison of FtsK sequences across species can identify:

  • Residues under positive selection (potentially species-specific functions)

  • Ultra-conserved residues (likely essential for core functions)

  • Variable regions (potentially dispensable or species-specific adaptations)

• Predicting regulatory mechanisms: Phylogenetic patterns in phosphorylation sites can predict regulatory mechanisms. For instance, if T318 is conserved across multiple Clostridial species, its phosphorylation likely represents a conserved regulatory mechanism .

• Identifying horizontal gene transfer: Phylogenetic analysis can detect horizontal gene transfer events. C. acetobutylicum contains operons shared with distantly related bacteria and archaea but not with B. subtilis, suggesting horizontal transfer . Such analysis can reveal unique evolutionary adaptations in FtsK.

Genome comparisons between C. acetobutylicum and B. subtilis show significant conservation of gene order , providing a foundation for comparative studies of FtsK function.

Can FtsK functional insights from model organisms be effectively translated to C. acetobutylicum systems?

Translating FtsK functional insights from model organisms to C. acetobutylicum requires careful consideration of both conserved and divergent features:

Aspects likely translatable from model organisms:

• Core motor function: The ATP-dependent DNA translocation mechanism is likely conserved across bacterial FtsK proteins

• General regulatory principles: The coordination between cell division and chromosome segregation represents a universal challenge for bacteria

• Experimental methodologies: Techniques developed for studying FtsK in model organisms (e.g., B. subtilis, E. coli) can often be adapted for C. acetobutylicum

Aspects requiring C. acetobutylicum-specific investigation:

• DNA sequence recognition: The specific DNA sequences recognized by the γ-subdomain of FtsK are likely species-specific

• Protein-protein interactions: The specific divisome components and chromosome segregation proteins that interact with FtsK may differ

• Regulatory mechanisms: While phosphorylation by PrkC appears to be a conserved regulatory mechanism in Clostridial species , the details of regulation may differ

The comparative analysis between C. acetobutylicum and B. subtilis genomes reveals both significant conservation of gene order and pronounced differences in many systems . This suggests that while core functions of FtsK are likely conserved, its integration into species-specific cellular processes requires dedicated study in C. acetobutylicum.

The successful application of genetic manipulation techniques developed for other Clostridial species to C. acetobutylicum supports the feasibility of translating experimental approaches across species.