Recombinant Arabidopsis thaliana RING-H2 finger protein ATL77 (ATL77)

What are the optimal expression systems for recombinant ATL77?

Recombinant ATL77 has been successfully expressed in E. coli with an N-terminal His-tag . When selecting an expression system for your research, consider the following methodological approaches:

• Bacterial expression (E. coli):

  • Advantages: High yield, cost-effective, and straightforward purification via His-tag

  • Limitations: Lacks post-translational modifications; protein may form inclusion bodies

  • Best for: Structural studies, in vitro enzyme assays, antibody production

• Plant expression systems:

  • Advantages: Native post-translational modifications; proper protein folding

  • Limitations: Lower yield; more complex purification

  • Best for: Functional studies requiring physiologically relevant modifications

• Cell-free expression systems:

  • Advantages: Rapid production; avoids toxicity issues

  • Limitations: Higher cost; lower yield

  • Best for: Producing proteins toxic to host cells or rapid screening

For functional studies of E3 ligase activity, consider that the structural basis of E2-E3 recognition has been elucidated for EL5 (a rice ATL protein) using NMR spectroscopy, demonstrating that the RING-H2 domain maintains similar structural features to previously characterized RING domains .

What are the recommended storage and handling protocols for recombinant ATL77?

Proper storage and handling of recombinant ATL77 is crucial for maintaining its stability and activity. Based on established protocols, the following methodological guidelines are recommended:

• Storage conditions:

  • Store lyophilized protein at -20°C to -80°C upon receipt

  • After reconstitution, store working aliquots at 4°C for up to one week

  • For long-term storage, add glycerol (final concentration 5-50%, with 50% being optimal) and store at -20°C to -80°C

  • Avoid repeated freeze-thaw cycles as they may compromise protein integrity

• Reconstitution protocol:

  • Briefly centrifuge the vial before opening to bring contents to the bottom

  • Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

  • The standard storage buffer contains Tris/PBS-based buffer with 6% Trehalose at pH 8.0

• Quality control indicators:

  • Purity: Greater than 90% as determined by SDS-PAGE

  • Functional assays: Consider ubiquitination assays to verify E3 ligase activity

How does ATL77 interact with E2 ubiquitin-conjugating enzymes?

Understanding the E2-E3 interaction is crucial for characterizing ATL77's ubiquitination mechanism. While specific information on ATL77-E2 interactions is limited in the provided search results, insights can be drawn from studies of related ATL family proteins:

• E2 partner preferences:

  • Studies with other ATL proteins show they typically rely on members of the Ubc4/Ubc5 subfamily of E2 conjugases

  • EL5, a rice ATL protein, has had its RING-H2 domain interaction with E2 enzymes characterized by NMR spectroscopy

• Interaction mechanisms:

  • Key amino acid residues for binding to E2 conjugases can be identified through mutagenesis studies of the RING-H2 domain

  • A strong correlation exists between E3 activity and the degree of interaction between the E2 enzyme and various RING domain mutants

• Electrostatic interactions:

  • Binding between RING E3 ligases and E2 enzymes can occur through electrostatic interactions

  • The arginine-rich region (region III) in ATLs may participate in these interactions, similar to how yeast Ubr1p (an E3) binds to Ubc2p (an E2) through a basic region in Ubr1p and an acidic region in Ubc2p

To experimentally investigate ATL77-E2 interactions, researchers could:

• Perform yeast two-hybrid or pull-down assays with various E2 enzymes

• Conduct mutagenesis studies of key residues in the RING-H2 domain

• Use structural biology approaches (X-ray crystallography or NMR) to characterize the interaction interface

What approaches can be used to identify potential substrates of ATL77?

Identifying the substrates of E3 ubiquitin ligases like ATL77 remains one of the major challenges in the field. Several methodological approaches can be employed:

• Protein interaction screening:

  • Yeast two-hybrid screening against Arabidopsis cDNA libraries

  • Co-immunoprecipitation followed by mass spectrometry (IP-MS)

  • Proximity-dependent biotin identification (BioID) or proximity ligation assay (PLA)

• Genetic approaches:

  • Analysis of atl77 knockout/knockdown phenotypes

  • Suppressor/enhancer genetic screens to identify genetic interactors

  • Comparison of transcriptome/proteome profiles between wild-type and atl77 mutant plants

• Ubiquitination assays:

  • In vitro ubiquitination assays with candidate substrates

  • Global proteomics to identify proteins with altered ubiquitination status in atl77 mutants

  • Ubiquitin remnant profiling (K-ε-GG) combined with quantitative proteomics

• Functional context analysis:

  • Since some ATL family members show early and transient responses to pathogen-associated molecular patterns (PAMPs) , focus on proteins involved in plant immune responses

  • Investigate proteins whose stability changes upon immune elicitation in wild-type versus atl77 mutant plants

Understanding the substrate specificity of ATL77 will provide crucial insights into its biological role and potential applications in plant biotechnology.

How can researchers design effective ubiquitination assays for ATL77?

Ubiquitination assays are essential for confirming E3 ligase activity and identifying substrates. Based on approaches used with other ATL proteins, the following methodology is recommended:

• In vitro ubiquitination assay components:

  • Purified components: E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme, preferably from the Ubc4/Ubc5 subfamily)

  • Recombinant ATL77 (His-tagged)

  • Ubiquitin (consider using tagged ubiquitin for easier detection)

  • ATP and appropriate buffer conditions

  • Potential substrate protein(s)

• Assay design considerations:

  • Controls: Reactions lacking E1, E2, E3 (ATL77), ATP, or ubiquitin

  • Mutant controls: RING-H2 domain mutants of ATL77 (based on conserved zinc-coordinating residues)

  • Time-course experiments to capture reaction kinetics

• Detection methods:

  • Western blotting using antibodies against ubiquitin or substrate

  • For multiple ubiquitination events, observe ladder-like patterns on Western blots

  • Mass spectrometry to identify ubiquitination sites (using GG-remnant antibodies)

• Advanced variations:

  • FRET-based assays for real-time monitoring

  • Analysis of different ubiquitin chain topologies (K48, K63, etc.)

  • Competition assays with other E3 ligases or substrates

The correlation between E3 activity and E2-E3 interaction observed with other ATL proteins suggests that optimizing the E2-ATL77 interaction is critical for successful ubiquitination assays .

How can researchers analyze the expression patterns and regulation of ATL77?

Understanding when and where ATL77 is expressed provides crucial insights into its biological function. Several approaches can be employed:

• Transcriptional analysis:

  • qRT-PCR to quantify ATL77 expression in different tissues or conditions

  • Promoter-reporter constructs (e.g., ATL77pro:GUS) to visualize spatial expression patterns

  • RNA-seq to compare expression across tissues, developmental stages, or stress conditions

• Protein-level analysis:

  • Western blotting using ATL77-specific antibodies

  • Creation of tagged versions (GFP, HA, FLAG) for visualization and immunoprecipitation

  • Immunohistochemistry to localize the protein in plant tissues

• Response to stimuli:

  • Some ATL family members show early and transient responses to PAMPs and can be induced by treatments such as cycloheximide

  • Monitor ATL77 expression following biotic stress (pathogens, PAMPs) and abiotic stress treatments

  • Analyze potential rapid degradation mechanisms, as some ATL transcripts have DST elements in their 3'UTR associated with transcript instability

• Regulatory elements:

  • Bioinformatic analysis of the ATL77 promoter for transcription factor binding sites

  • Chromatin immunoprecipitation (ChIP) to identify proteins binding to the ATL77 promoter

  • Analysis of epigenetic modifications at the ATL77 locus

Studies with other ATL family members show that their transcripts can be rapidly induced and have short half-lives, which may also be true for ATL77 .

What structural analyses can be performed to understand ATL77's function?

Structural characterization of ATL77 can provide insights into its function, substrate recognition, and potential for targeted modifications. Consider the following methodological approaches:

• Domain-specific structural analyses:

  • NMR spectroscopy of the RING-H2 domain, similar to studies performed with the rice ATL protein EL5

  • X-ray crystallography of ATL77 alone or in complex with E2 enzymes

  • Cryo-EM for larger complexes involving ATL77

• Computational structure prediction and analysis:

  • Homology modeling based on related RING-H2 domain structures

  • Molecular dynamics simulations to understand flexibility and potential binding interfaces

  • Protein-protein docking with potential E2 partners or substrates

• Functional mapping through mutagenesis:

  • Targeted mutations of zinc-coordinating residues in the RING-H2 domain

  • Alanine scanning of the hydrophobic region or GLD domain

  • Creation of chimeric proteins with other ATL family members to map functional regions

• Topology and membrane association studies:

  • Protease protection assays to determine membrane topology

  • Fluorescence microscopy with domain-specific tags

  • Membrane fractionation studies to confirm localization

The analysis of EL5's RING-H2 domain showed that it maintains structural features similar to other characterized RING domains, suggesting ATL77's RING-H2 domain likely adopts a similar fold with specific residues critical for E2 binding .

How does ATL77 compare with other ATL family members in Arabidopsis and other species?

The ATL family is remarkably diverse, with 80 members identified in Arabidopsis thaliana and 121 in Oryza sativa . Understanding ATL77's relationship to other family members provides evolutionary context and functional insights:

• Phylogenetic analysis:

  • Position of ATL77 within the ATL family phylogeny

  • Identification of closest homologs in Arabidopsis and other plant species

  • Correlation between phylogenetic clustering and functional specialization

• Structural comparisons:

  • Conservation analysis of the RING-H2 domain, hydrophobic region, and GLD domain

  • Presence of additional domains or motifs specific to ATL77 or shared with close relatives

  • Comparison of 3D structures (predicted or determined) between ATL77 and other characterized ATLs

• Functional divergence:

  • Differential expression patterns among ATL family members

  • Substrate specificity differences

  • Roles in distinct biological processes (e.g., immunity, development, abiotic stress responses)

• Evolutionary history:

  • Analysis of selection pressures (Ka/Ks ratios) acting on different domains

  • Identification of ATL77 orthologs in other plant species

  • Investigation of gene duplication events leading to ATL77

The large number of ATL family members (80 in Arabidopsis) suggests functional diversification, with different members potentially targeting distinct substrates or functioning in different cellular contexts .

What roles do ATL family proteins play in plant immunity and stress responses?

Several ATL family members have been implicated in plant immunity and stress responses, which provides context for investigating ATL77's potential roles:

• Response to pathogen challenges:

  • Some ATL family members show early and transient responses to PAMPs

  • For example, AthATL2 induction is independent of de novo protein synthesis, and its transcript has a short half-life

  • ACRE-132, a tobacco ATL gene, is induced within 30 minutes after treatment with fungal effectors

• Potential immune-related functions:

  • Regulation of defense protein stability through ubiquitination

  • Modulation of pattern recognition receptor (PRR) levels or signaling components

  • Targeting of negative regulators of immunity for degradation

• Methodological approaches to study ATL77 in immunity:

  • Pathogen infection assays comparing wild-type and atl77 mutant plants

  • Quantification of defense markers (ROS, callose, defense genes) in mutant backgrounds

  • Identification of changes in the ubiquitinome following pathogen challenge

• Abiotic stress connections:

  • E3 ligases often function in multiple stress response pathways

  • Analyze ATL77 expression under various abiotic stresses (drought, salt, cold)

  • Investigate physiological parameters and stress tolerance in atl77 mutants

Given that other ATL family members respond rapidly to immune elicitors, ATL77 may have a similar role in early defense responses, potentially by regulating the stability of key immune components .

What emerging technologies can advance ATL77 research?

Several cutting-edge technologies hold promise for deepening our understanding of ATL77 function:

• CRISPR/Cas9 genome editing:

  • Generation of precise mutations in ATL77 to study specific domains or residues

  • Creation of reporter knock-ins for live visualization of expression

  • Base editing to introduce specific amino acid changes without disrupting the gene

• Advanced protein interaction methods:

  • Proximity labeling approaches (BioID, TurboID, APEX)

  • Single-molecule pull-down (SiMPull) for analyzing complex stoichiometry

  • Förster Resonance Energy Transfer (FRET) for monitoring dynamic interactions

• Proteomics innovations:

  • Targeted proteomics to quantify low-abundance proteins in specific contexts

  • Ubiquitin-remnant profiling combined with SILAC or TMT labeling

  • Cross-linking mass spectrometry (XL-MS) to map interaction interfaces

• Structural biology advances:

  • AlphaFold2 or RoseTTAFold for protein structure prediction

  • Cryo-electron microscopy for complex structures

  • Time-resolved X-ray crystallography for capturing dynamic states

• Single-cell approaches:

  • Single-cell RNA-seq to capture cell-type-specific expression patterns

  • Single-cell proteomics to analyze protein-level variation

  • Spatial transcriptomics to map expression in tissue contexts

Implementing these technologies could help overcome current limitations in understanding ATL77's biological functions and regulatory mechanisms.

How can researchers integrate multi-omics data to understand ATL77 function in plant systems?

A comprehensive understanding of ATL77 requires integration of multiple data types:

• Integrative data analysis approaches:

  • Correlation of transcriptomics, proteomics, and ubiquitinomics data

  • Network analysis to position ATL77 in protein-protein interaction or gene regulatory networks

  • Multivariate statistical methods to identify patterns across datasets

• Systems biology modeling:

  • Mathematical modeling of ubiquitination dynamics

  • Prediction of system-wide effects of ATL77 perturbation

  • Integration of ATL77 into existing plant immune system models

• Methodological framework for data integration:

  • Collection of paired samples for multi-omics analysis

  • Consistent experimental designs across platforms

  • Comprehensive metadata collection for accurate cross-experiment comparison

• Data visualization and exploration tools:

  • Interactive visualization of ATL77-centered networks

  • Temporal profiling of molecular changes following ATL77 perturbation

  • Spatial mapping of ATL77 activity in different cell types or tissues

The integration of multiple data types will provide a holistic view of ATL77's function in plant development, immunity, and stress responses, moving beyond single-molecule studies to understand its role in broader cellular and organismal contexts.