Recombinant Arabidopsis thaliana RING-H2 finger protein ATL34 (ATL34)

What is Recombinant Arabidopsis thaliana RING-H2 finger protein ATL34?

Recombinant Arabidopsis thaliana RING-H2 finger protein ATL34 (ATL34) is a protein belonging to the RING/U-box superfamily that functions as a RING-type E3 ubiquitin transferase . The protein is encoded by the AT1G35330 gene (also known as T9I1.10 or T9I1_10) in Arabidopsis thaliana . As a member of the ATL (Arabidopsis Tóxicos en Levadura) family, it contains a characteristic RING-H2 zinc finger domain that is essential for its E3 ligase activity. For research applications, the protein can be recombinantly produced in various expression systems including E. coli, yeast, baculovirus, or mammalian cells, allowing researchers to study its structure, function, and interactions in controlled experimental settings .

What is the protein structure and sequence of mature ATL34?

The mature ATL34 protein consists of amino acids 27-327 of the full protein sequence . The complete amino acid sequence of the mature protein is: QHQPRTTAPPYIAQRPNQVPAVIIAMLMFTLLFSMLACCVCYKYTNTSPHGTSSDTEEGG HGEVAFTRRTSRGLGKDVINSFPSFLYSQVKGLKIGKGGVECAICLNEFEDEETLRLMPP CSHAFHASCIDVWLSSRSTCPVCRASLPPKPGSDQNSLYPFIRPHDNQDMDLENVTARRS VLESPDVRLLDRLSWSNNTGANTPPRSRSTGLSNWRITELLFPRSHSTGHSLVPRVENLD RFTLQLPEEVRRQLSHMKTLPQARSSREGYRSGSVGSERRGKGKEKEFGEGSFDRLKAEM V . Within this sequence, the RING-H2 domain can be identified by the characteristic cysteine and histidine residues forming the zinc coordination sites, particularly in the region containing the ECAICLNEFEDEETLRLMPPCSHAFHASCIDVWLSSRSTCPVCRA sequence. This domain is critical for the protein's E3 ubiquitin ligase function, as it mediates interactions with E2 ubiquitin-conjugating enzymes.

What expression systems are used for producing recombinant ATL34?

Recombinant ATL34 can be expressed in multiple heterologous systems, with each offering distinct advantages depending on the research objectives. The protein can be produced in E. coli, yeast, baculovirus-infected insect cells, or mammalian cell systems . For structural studies and basic biochemical characterization, E. coli expression is commonly employed due to its high yield and cost-effectiveness. The search results indicate that commercially available recombinant full-length ATL34 is typically expressed in E. coli with an N-terminal His-tag to facilitate purification . For studies requiring post-translational modifications or more native-like protein folding, eukaryotic expression systems such as yeast or baculovirus may be preferable. When selecting an expression system, researchers should consider factors such as protein solubility, activity requirements, and downstream applications.

What is the subcellular localization of ATL34 in Arabidopsis thaliana?

While the search results don't directly specify the subcellular localization of ATL34, analysis of its sequence provides important clues. The protein contains a transmembrane domain in its N-terminal region (visible in the sequence as the hydrophobic stretch "VIIAMLMFTLLFSMLACCVCYKY"), suggesting membrane association . Many RING-type E3 ubiquitin ligases, particularly those in the ATL family, are known to localize to cellular membranes, often the endoplasmic reticulum or plasma membrane. To experimentally determine ATL34 localization, researchers typically employ approaches such as fluorescent protein tagging followed by confocal microscopy, subcellular fractionation combined with immunoblotting, or immunohistochemistry with specific antibodies against ATL34. The specific membrane localization could provide insights into the protein's function in cellular signaling or protein quality control pathways.

What are the key functional domains in ATL34?

ATL34 contains several key functional domains that are critical for its activity as an E3 ubiquitin ligase. The most prominent is the RING-H2 finger domain, characterized by a specific pattern of cysteine and histidine residues that coordinate two zinc ions . This domain is essential for the protein's catalytic activity, mediating interactions with E2 ubiquitin-conjugating enzymes. The N-terminal region contains a transmembrane domain (approximately amino acids 31-53: VIIAMLMFTLLFSMLACCVCYKY), which likely anchors the protein to cellular membranes . Additionally, ATL34 may contain substrate recognition motifs and regulatory regions that control its activity and specificity. Understanding these domains is crucial for designing experiments to study ATL34 function, as mutations in these regions can significantly affect protein activity, localization, and interaction capabilities.

What is the mechanism of ATL34's E3 ubiquitin ligase activity?

As a RING-type E3 ubiquitin ligase, ATL34 functions as a scaffold that brings together an E2 ubiquitin-conjugating enzyme and a substrate protein . The RING-H2 domain of ATL34 is crucial for this activity, as it directly interacts with the E2 enzyme. The catalytic mechanism involves the E2 enzyme transferring an activated ubiquitin molecule to a lysine residue on the substrate protein, with ATL34 facilitating this transfer without forming a covalent bond with ubiquitin itself. To study this activity experimentally, researchers can perform in vitro ubiquitination assays using purified recombinant ATL34, an E2 enzyme, ubiquitin (often fluorescently labeled), ATP, and potential substrate proteins. Detection methods include SDS-PAGE followed by western blotting or fluorescence scanning to visualize ubiquitinated products. Site-directed mutagenesis of conserved residues in the RING-H2 domain can help identify amino acids critical for E3 ligase activity.

How does ATL34 select its substrate proteins?

Substrate recognition by ATL34 likely involves specific protein-protein interaction motifs that are distinct from its RING-H2 domain. While the search results don't provide specific information on ATL34 substrates, understanding substrate selection is crucial for characterizing its cellular function . Methodologically, researchers can identify potential substrates through approaches such as yeast two-hybrid screening, co-immunoprecipitation followed by mass spectrometry, or proximity-dependent biotin labeling (BioID or TurboID). Validation of potential substrates typically involves demonstrating direct interaction with ATL34, showing ubiquitination in vitro and in vivo, and observing stabilization of the substrate protein when ATL34 is depleted or inactivated. Comparative analysis with other ATL family members can also provide insights, as substrate specificity often diverges among related E3 ligases despite conserved catalytic mechanisms.

What role does ATL34 play in plant stress responses?

Many RING-type E3 ubiquitin ligases in plants, including several ATL family members, function in stress response pathways by regulating the abundance of key signaling components. While specific information about ATL34's role in stress responses is not detailed in the search results, investigating this function would involve several experimental approaches . Researchers could analyze ATL34 expression levels under various stress conditions (drought, salinity, pathogen infection, etc.) using qRT-PCR or RNA-seq. Phenotypic analysis of ATL34 knockout or overexpression plants under stress conditions could reveal functional relevance. Identification of ATL34 substrates that accumulate during stress responses would provide mechanistic insights. Additionally, comparative analysis with other stress-responsive E3 ligases could help position ATL34 within stress signaling networks. The transmembrane domain suggests potential involvement in membrane-associated stress signaling pathways.

How is ATL34 itself regulated at the post-translational level?

E3 ubiquitin ligases like ATL34 are often themselves subject to tight regulation through post-translational modifications. While the search results don't specify regulatory mechanisms for ATL34, investigating this aspect is important for understanding its function . Common regulatory mechanisms for RING-type E3 ligases include phosphorylation, which can alter activity or substrate specificity; auto-ubiquitination, which can lead to self-regulation through proteasomal degradation; and protein-protein interactions that might inhibit or enhance ligase activity. Methodologically, researchers can identify post-translational modifications using mass spectrometry of purified ATL34 under different conditions. Mutagenesis of modified residues followed by activity assays can establish the functional significance of these modifications. Interaction studies with potential regulatory proteins could reveal additional layers of control. The stability and turnover rate of ATL34 itself can be measured using cycloheximide chase assays.

What are the phenotypic consequences of ATL34 overexpression or knockout?

Understanding the phenotypic effects of altered ATL34 expression provides insights into its physiological significance. To investigate this, researchers can generate transgenic Arabidopsis lines overexpressing ATL34 or knockout lines using T-DNA insertion or CRISPR-Cas9 gene editing. These lines would be characterized for alterations in growth, development, and responses to various environmental conditions. Key parameters to assess include germination rate, root and shoot growth, flowering time, seed yield, and stress tolerance. Molecular phenotyping through transcriptomics (RNA-seq) or proteomics can reveal downstream pathways affected by ATL34 activity. Complementation assays, where wild-type ATL34 is reintroduced into knockout lines, can confirm phenotype specificity. Additionally, expression of catalytically inactive ATL34 (with mutations in the RING-H2 domain) can distinguish between ubiquitination-dependent and independent functions.

What are the optimal conditions for recombinant ATL34 expression and purification?

For optimal expression and purification of recombinant ATL34, researchers should consider several key parameters. Based on commercial production methods, E. coli appears to be a suitable expression system for obtaining functional protein . The mature protein (amino acids 27-327) with an N-terminal His-tag is commonly used . For expression, induction conditions (IPTG concentration, temperature, duration) should be optimized to maximize soluble protein yield. For purification, immobilized metal affinity chromatography (IMAC) using the His-tag is the primary step, followed by additional purification if needed (ion exchange or size exclusion chromatography). According to provided information, the purified protein should have >90% purity as determined by SDS-PAGE . After purification, the protein is typically stored in a Tris/PBS-based buffer with 6% trehalose at pH 8.0 . For long-term storage, the recommendation is to add glycerol to a final concentration of 5-50% (with 50% being commonly used) and store aliquots at -20°C or -80°C .

How should researchers handle and store recombinant ATL34 to maintain activity?

Proper handling and storage of recombinant ATL34 is crucial for maintaining its activity. After purification, the protein is typically provided as a lyophilized powder or in a liquid buffer containing glycerol . For reconstitution of lyophilized protein, it should be briefly centrifuged before opening the vial, then dissolved in deionized sterile water to a concentration of 0.1-1.0 mg/mL . For storage, the recommended conditions are -20°C or -80°C for long-term preservation, with the addition of glycerol (5-50% final concentration) to prevent freeze-thaw damage . Working aliquots can be stored at 4°C for up to one week . Importantly, repeated freeze-thaw cycles should be avoided as they can lead to protein denaturation and activity loss . For experiments requiring active protein, it's advisable to thaw aliquots quickly at room temperature or in a water bath at 25°C, keep on ice during experiments, and avoid multiple freeze-thaw cycles by preparing single-use aliquots.

What assays can be used to measure ATL34 E3 ubiquitin ligase activity?

Several assays can be employed to measure the E3 ubiquitin ligase activity of ATL34. The most direct approach is an in vitro ubiquitination assay, which requires purified recombinant ATL34, an appropriate E2 ubiquitin-conjugating enzyme, ubiquitin (which can be tagged with fluorescent labels or epitope tags for detection), ATP, and potential substrate proteins. The reaction products are typically analyzed by SDS-PAGE followed by western blotting or fluorescence scanning to detect ubiquitinated species. Auto-ubiquitination assays, where ATL34 catalyzes its own ubiquitination, can serve as a control for activity in the absence of known substrates. For cellular assays, substrate stability assays can be performed where the degradation rate of a putative substrate is measured in the presence or absence of functional ATL34. Ubiquitin chain linkage analysis using linkage-specific antibodies or mass spectrometry can provide insights into the type of ubiquitin chains formed (K48, K63, etc.), which often correlate with different cellular outcomes.

What approaches are effective for identifying ATL34 substrates and interaction partners?

Identifying the substrates and interaction partners of ATL34 is crucial for understanding its biological function. Several complementary approaches can be employed for this purpose. Yeast two-hybrid screening offers a high-throughput method to identify direct protein-protein interactions, though it may miss interactions requiring post-translational modifications. Affinity purification coupled with mass spectrometry (AP-MS) using tagged ATL34 as bait can capture both direct and indirect interaction partners. Proximity-dependent biotin labeling methods (BioID, TurboID) can identify proteins in close proximity to ATL34 in living cells. For substrate identification specifically, researchers can perform proteomics analysis comparing protein abundance in wild-type versus ATL34 knockout plants, potentially with proteasome inhibition to stabilize ubiquitinated substrates. Validation of potential substrates should include demonstration of direct interaction, in vitro and in vivo ubiquitination, and altered stability in the presence or absence of functional ATL34.

How can researchers design effective ATL34 mutants for functional studies?

Designing effective mutants is essential for dissecting ATL34 function. Several strategic mutations can provide valuable insights: (1) RING-H2 domain mutations - substituting conserved cysteine or histidine residues in the RING-H2 domain (identifiable in the sequence: ECAICLNEFEDEETLRLMPPCSHAFHASCIDVWLSSRSTCPVCRA) with alanine will disrupt zinc coordination and abolish E3 ligase activity, creating a catalytically inactive mutant ; (2) Transmembrane domain mutations - altering the hydrophobic residues in the transmembrane region (VIIAMLMFTLLFSMLACCVCYKY) can affect membrane localization and function ; (3) Substrate binding region mutations - once substrate interaction regions are identified, mutations in these areas can create substrate-specific binding mutants; (4) Phosphorylation site mutations - if regulatory phosphorylation sites are identified, phosphomimetic (S/T to D/E) or phosphodeficient (S/T to A) mutations can probe their functional significance. Each mutant should be carefully characterized for expression, stability, localization, and activity using the methods described in previous sections.

How can researchers optimize western blot detection of ATL34 and its ubiquitinated targets?

Optimizing western blot detection for ATL34 and its ubiquitinated targets requires careful consideration of several factors. For detecting ATL34 itself, researchers can use antibodies against the native protein or against tags like the N-terminal His-tag commonly used in recombinant versions . When detecting ubiquitinated substrates, sample preparation is crucial—additions of deubiquitinase inhibitors (like N-ethylmaleimide or PR-619) and proteasome inhibitors (MG132) to lysis buffers help preserve ubiquitinated species. Denaturing conditions (8M urea or 1% SDS) in lysis buffers can disrupt protein-protein interactions and improve detection of ubiquitinated proteins. For blotting, PVDF membranes are generally preferred over nitrocellulose for ubiquitin detection due to better protein retention. When analyzing results, ubiquitinated proteins typically appear as higher molecular weight species or smears above the unmodified protein band. Controls should include catalytically inactive ATL34 mutants and samples with proteasome inhibition to accumulate ubiquitinated proteins.

What are common issues in ATL34 expression and purification and how can they be addressed?

Researchers may encounter several challenges when expressing and purifying ATL34. Insolubility is a common issue, particularly due to the transmembrane domain . This can be addressed by optimizing expression conditions (lower temperature, reduced inducer concentration), using solubility tags (MBP, SUMO), or employing detergents during purification. Protein degradation during expression or purification can be minimized by including protease inhibitors and working at lower temperatures. Low yield might be improved by optimizing codon usage for the expression host, using stronger promoters, or trying different expression systems. Inactive protein could result from improper folding; slower induction at lower temperatures often helps. For purification, non-specific binding to affinity resins can be reduced by including low concentrations of imidazole in wash buffers when using His-tag purification. Aggregation during storage can be prevented by optimizing buffer conditions, adding stabilizers like trehalose (6%) as mentioned in the product specifications, and storing with glycerol (5-50%) .

How can contradictory results in ATL34 substrate identification be reconciled?

When faced with contradictory results in ATL34 substrate identification studies, researchers should systematically evaluate and reconcile discrepancies through several approaches. First, experimental conditions should be carefully compared—differences in cell types, developmental stages, or stress conditions can significantly affect E3 ligase-substrate interactions. Second, the methods used for detection might have different sensitivities or biases; for example, mass spectrometry might identify interactions missed by yeast two-hybrid screens. Third, the specific ATL34 construct used (full-length vs. truncated, tagged vs. untagged) could affect substrate recognition . Fourth, the absence of necessary cofactors or post-translational modifications in certain experimental systems might prevent substrate recognition. To resolve contradictions, researchers should perform validation studies using multiple complementary approaches, ideally in systems that closely mimic the native context. Quantitative methods like quantitative proteomics or real-time measurements of substrate stability can help clarify ambiguous results.

What controls are essential for ATL34 functional studies?

When conducting functional studies with ATL34, several essential controls should be included to ensure result validity. For E3 ligase activity assays, a catalytically inactive mutant (with mutations in the RING-H2 domain) serves as a negative control . Reactions lacking ATP or E2 enzyme provide additional negative controls by preventing ubiquitin activation. For interaction studies, controls should include unrelated proteins of similar size and cellular localization to rule out non-specific binding. In cellular or plant-based studies, appropriate genetic controls are crucial: wild-type plants, ATL34 knockout lines, and complemented lines (knockout expressing wild-type ATL34) allow for phenotype validation. When studying substrate degradation, proteasome inhibitors (like MG132) can confirm the ubiquitin-proteasome pathway involvement. Time-course experiments should include time-zero controls. For specificity assessment, closely related ATL family members can serve as comparisons to determine unique versus shared functions of ATL34.

How can researchers integrate ATL34 data with broader plant ubiquitination networks?

Integrating ATL34 research into the broader context of plant ubiquitination networks requires systematic data collection and analysis approaches. Researchers can start by comparing ATL34 substrates and interactors with those of other plant E3 ligases, particularly other ATL family members, to identify unique and overlapping functions. Network analysis tools can visualize these relationships and identify central nodes or pathways. Integration with transcriptomics data from ATL34 mutant lines can reveal downstream effects of ATL34 activity on gene expression. Pathway enrichment analysis of ATL34-affected proteins can place its function in specific cellular processes. Comparative analysis across plant species can identify evolutionarily conserved ATL34 functions. For data integration, researchers can utilize plant-specific databases like TAIR (The Arabidopsis Information Resource), as well as protein interaction databases like STRING or BioGRID. Publishing datasets in standardized formats and repositories ensures that ATL34 data can be incorporated into future meta-analyses and systems biology approaches.