Phospho-GRIA4 (S862) Antibody

What is GRIA4 and what is its functional significance in neuronal signaling?

GRIA4 (also known as GluR4 or GluA4) encodes the glutamate receptor 4, an AMPA receptor subunit that functions as a ligand-gated ion channel in the central nervous system. This receptor plays a critical role in excitatory synaptic transmission. The binding of L-glutamate, which acts as an excitatory neurotransmitter at many synapses, induces a conformational change in the receptor. This leads to the opening of the cation channel, converting chemical signals to electrical impulses by allowing the entry of monovalent and divalent cations such as sodium and calcium .

GRIA4 is particularly important for learning and memory processes. Upon activation, the receptor rapidly desensitizes and enters a transient inactive state, characterized by the presence of bound agonist. In the presence of calcium channel subunits like CACNG4, CACNG7, or CACNG8, GRIA4 shows resensitization, which is characterized by a delayed accumulation of current flux upon continued application of glutamate .

Why is the phosphorylation at serine 862 (S862) of GRIA4 significant?

Phosphorylation at S862 in GRIA4 represents a critical regulatory mechanism for receptor function and trafficking. This specific post-translational modification appears to be involved in stabilizing the receptor's surface expression. The phosphorylation state of S862 modulates protein-protein interactions that control GRIA4 localization and activity at synapses .

Research indicates that PKC (Protein Kinase C) phosphorylation at this site inhibits calmodulin (CaM) binding, thereby increasing GRIA4 surface expression. This phosphorylation event appears to work in concert with PDZ domain-containing proteins like PICK1, which help stabilize the receptor at the cell surface . The dynamic regulation of GRIA4 phosphorylation at S862 likely contributes to synaptic plasticity mechanisms underlying learning and memory.

How does GRIA4 relate to neurological disorders?

Recent research has identified de novo variants in GRIA4 that are associated with intellectual disability with or without seizures, gait abnormalities, and problems with social behavior . Specifically, five unrelated individuals with intellectual disability were found to have de novo heterozygous pathogenic variants in GRIA4.

Four of these variants are located in the highly conserved SYTANLAAF motif in the transmembrane protein M3, which is critical for receptor function. Molecular modeling showed that three of the variants in this motif orient toward the center of the pore region and likely disturb the gating mechanism. The fourth variant in the SYTANLAAF motif likely results in reduced permeability .

The importance of GRIA4 in neuronal function, coupled with data on other glutamate receptor subunits, suggests that pathogenic variants in GRIA4 exert their effects through dominant functional mechanisms rather than simple loss of function.

What are the optimal storage conditions for Phospho-GRIA4 (S862) Antibody?

For long-term storage, Phospho-GRIA4 (S862) Antibody should be stored at -20°C or -80°C upon receipt. Repeated freeze-thaw cycles should be avoided as they can compromise antibody activity .

For short-term storage and frequent use, the antibody can be stored at 4°C for up to one month . The antibody is typically supplied in a liquid form in PBS containing 50% glycerol, 0.5% BSA, and 0.02% sodium azide as a preservative .

What applications has Phospho-GRIA4 (S862) Antibody been validated for?

Based on the available information, Phospho-GRIA4 (S862) Antibody has been validated for the following applications:

The antibody demonstrates reactivity across multiple species including Human, Mouse, and Rat .

Western blot analysis has confirmed antibody specificity using lysates from HepG2 cells treated with Forskolin (40nM for 30 minutes), where blocking with the phospho-peptide confirms specificity. Immunohistochemistry validation has been performed using paraffin-embedded human brain tissue, with appropriate controls using phospho-peptide blocking .

How should samples be prepared for optimal detection of phosphorylated GRIA4?

For optimal detection of phosphorylated GRIA4 at S862, the following sample preparation guidelines should be considered:

• Western Blotting: Samples should be lysed in buffer containing phosphatase inhibitors to preserve the phosphorylation state. Treating cells with phosphorylation-inducing agents like Forskolin (40nM for 30 minutes) can be used as a positive control .

• Immunohistochemistry: For paraffin-embedded tissues, standard antigen retrieval techniques should be applied. Phosphatase inhibitors should be included in all buffers used during tissue processing and antigen retrieval .

• ELISA: Sample preparation protocols should include steps to maintain phosphorylation status through the use of phosphatase inhibitors and appropriate blocking agents to reduce background.

For all applications, it's essential to include appropriate controls, such as:

• Samples blocked with the specific phospho-peptide used as the immunogen

• Samples treated with phosphatase to demonstrate specificity for the phosphorylated form

• Comparison with non-phospho-specific GRIA4 antibodies to confirm total protein levels

How can I confirm the specificity of Phospho-GRIA4 (S862) Antibody in my experiments?

Confirming specificity of the Phospho-GRIA4 (S862) Antibody is critical for reliable research outcomes. Several methods can be employed:

• Peptide Competition Assay: Pre-incubate the antibody with the phosphorylated peptide used as the immunogen. The specific signal should be abolished or significantly reduced. This approach has been validated in both Western blot and immunohistochemistry applications .

• Phosphatase Treatment: Treat one sample with lambda phosphatase before probing with the antibody. Signal loss after phosphatase treatment confirms specificity for the phosphorylated epitope.

• Induction of Phosphorylation: Compare samples with and without treatments known to induce phosphorylation at S862, such as PKC activators. For example, Forskolin treatment (40nM for 30 minutes) has been shown to increase phosphorylation at this site .

• Genetic Controls: Where possible, use GRIA4 knockout tissues or cells as negative controls, or cells expressing GRIA4 with a S862A mutation that prevents phosphorylation at this site.

What factors might affect phosphorylation status of GRIA4 at S862?

Several factors can influence the phosphorylation status of GRIA4 at S862, which should be considered when designing experiments and interpreting results:

• PKC Activity: Protein Kinase C (PKC) phosphorylates S862 on GRIA4. Factors affecting PKC activity, such as calcium levels, diacylglycerol, or phorbol esters, will impact S862 phosphorylation .

• PICK1 Interaction: The PDZ domain-containing protein PICK1 has been shown to work with PKC to regulate GRIA4 phosphorylation. In mice lacking PICK1, PKC-dependent increases in receptor phosphorylation and surface expression are diminished .

• Calmodulin Binding: Phosphorylation at S862 inhibits calmodulin (CaM) binding. Conditions affecting calmodulin availability or activity will indirectly influence the detected levels of phosphorylated GRIA4 .

• Sample Handling: Phosphorylation states can be rapidly altered during sample preparation. Using phosphatase inhibitors in all buffers is essential to preserve the in vivo phosphorylation state.

• Neuronal Activity: Synaptic activity and glutamatergic signaling can modulate phosphorylation events. The physiological state of neurons in the experimental model will influence baseline levels of S862 phosphorylation.

How does GRIA4 phosphorylation at S862 regulate receptor trafficking and synaptic function?

Phosphorylation of GRIA4 at S862 plays a crucial role in regulating receptor trafficking and synaptic function through multiple mechanisms:

• Surface Stabilization: Phosphorylation at S862 increases GRIA4 surface expression by preventing receptor internalization. This phosphorylation event works in concert with PICK1 binding to stabilize the receptor on the cell surface .

• Inhibition of Calmodulin Binding: S862 phosphorylation inhibits calmodulin (CaM) binding to GRIA4, which is a key regulatory mechanism. When calmodulin cannot bind, the receptor remains more stable at the cell surface .

• PKC-PICK1 Interaction: Research shows that PKC phosphorylation and PICK1 binding act cooperatively to regulate GRIA4. In mice lacking PICK1, PKC-dependent increases in GRIA4 phosphorylation and surface expression are diminished .

• Synaptic Plasticity: The dynamic regulation of GRIA4 surface expression through phosphorylation at S862 contributes to certain forms of hippocampal synaptic plasticity. In particular, mGluR7-dependent plasticity at mossy fiber-interneuron hippocampal synapses is impaired in mice lacking PICK1, suggesting a functional relationship between metabotropic glutamate receptor signaling and AMPA receptor phosphorylation .

What is the relationship between de novo GRIA4 variants and neurological phenotypes?

Research has identified several de novo variants in GRIA4 associated with neurological disorders. These variants provide insight into the structure-function relationships of the receptor:

• SYTANLAAF Motif Variants: Four pathogenic variants have been identified within the highly conserved SYTANLAAF motif in the transmembrane protein M3 of GRIA4: p.Thr639Ser, p.Asn641Asp, p.Ala643Gly, and p.Ala644Val. Molecular modeling indicates that three of these variants orient toward the center of the pore region and likely disturb the gating mechanism, while the fourth likely results in reduced permeability .

• Extracellular Domain Variant: The p.Arg697Pro variant occurs in an extracellular domain and potentially interferes with binding between monomers. This variant leads to the disruption of an α helix, potentially causing local unwinding and interfering with binding between monomers .

• Genotype-Phenotype Correlation: There appears to be some degree of genotype-phenotype correlation. The individual with the p.Arg697Pro variant outside the SYTANLAAF motif presented with a milder phenotype, while those with variants within the motif showed more severe symptoms. Even within the motif, the variant at position 639 (which has a lesser effect on structural destabilization) was found in an individual with milder symptoms .

• Dominant Functional Effect: The available data suggests that the pathogenic effect of these variants is due to a dominant functional effect rather than simple loss of function. This aligns with findings related to other glutamate receptor variants .

How does the phosphorylation of GRIA4 at S862 interact with other post-translational modifications and protein binding partners?

The phosphorylation of GRIA4 at S862 is part of a complex regulatory network involving multiple post-translational modifications and protein interactions:

• PKC Phosphorylation and PICK1 Binding: These two mechanisms work cooperatively to stabilize GRIA4 on the cell surface. Research shows that PKC-dependent increases in GRIA4 phosphorylation and surface expression are diminished in mice lacking PICK1, indicating a coordinated regulatory mechanism .

• Calmodulin Competition: Phosphorylation at S862 inhibits calmodulin binding to GRIA4. This competitive interaction represents a regulatory switch that determines receptor trafficking dynamics .

• PDZ Domain Interactions: The C-terminal PDZ ligand of GRIA4 interacts with PDZ domain-containing proteins like PICK1. These interactions are influenced by the phosphorylation state of the receptor and contribute to its localization and functional properties .

• Metabotropic Glutamate Receptor Crosstalk: Studies suggest a functional relationship between GRIA4 and metabotropic glutamate receptors, particularly mGluR7. The trafficking mechanisms regulated by S862 phosphorylation may be integrated with signaling from these receptors, as evidenced by impaired mGluR7-dependent plasticity in PICK1 knockout mice .

Understanding these complex interactions provides insight into the molecular mechanisms underlying synaptic plasticity and may inform therapeutic strategies for neurological disorders associated with glutamate receptor dysfunction.

What are the best practices for using Phospho-GRIA4 (S862) Antibody in Western blotting?

For optimal Western blotting results with Phospho-GRIA4 (S862) Antibody, follow these research-validated protocols:

• Sample Preparation:

  • Use fresh tissue or cells when possible

  • Lyse samples in buffer containing phosphatase inhibitors (e.g., sodium fluoride, sodium orthovanadate)

  • For positive controls, treat cells with PKC activators or Forskolin (40nM for 30 minutes)

• Antibody Dilution and Incubation:

  • Use the antibody at 1:500-1:2000 dilution

  • Incubate membranes overnight at 4°C for best results

  • Use 5% BSA in TBST for antibody dilution rather than milk, as milk contains phosphatases

• Validation Controls:

  • Run a peptide competition assay by pre-incubating the antibody with the phosphorylated peptide immunogen

  • Include phosphatase-treated samples as negative controls

  • Compare results with a total GRIA4 antibody to normalize for total protein expression

• Detection Considerations:

  • GRIA4 has a molecular weight of approximately 100 kDa

  • Use standard ECL detection methods or fluorescent secondary antibodies

  • For quantification, ensure signals are within the linear range of detection

How can I optimize immunohistochemistry protocols using Phospho-GRIA4 (S862) Antibody?

To achieve optimal immunohistochemistry results with Phospho-GRIA4 (S862) Antibody, consider these specialized approaches:

• Tissue Preparation and Fixation:

  • Perfusion fixation with 4% paraformaldehyde is recommended for brain tissue

  • For paraffin embedding, minimize fixation time to preserve phospho-epitopes

  • Include phosphatase inhibitors in all buffers during tissue processing

• Antigen Retrieval:

  • Heat-induced epitope retrieval in citrate buffer (pH 6.0) is generally effective

  • Optimize retrieval time and temperature for your specific tissue type

• Antibody Application:

  • Use at 1:100-1:300 dilution as recommended

  • Incubate overnight at 4°C in a humidified chamber

  • Use appropriate blocking solutions containing BSA rather than milk proteins

• Controls and Validation:

  • Include peptide competition controls by pre-incubating the antibody with phospho-peptide

  • Compare staining patterns with total GRIA4 antibody

  • Consider dual-labeling with neuronal markers to confirm cellular localization

• Signal Development and Analysis:

  • For chromogenic detection, DAB can be used with appropriate enhancement if needed

  • For fluorescent detection, tyramide signal amplification may improve sensitivity

  • Evaluate specificity through the absence of signal in peptide-blocked controls

These methodological approaches will help ensure specific and reliable detection of phosphorylated GRIA4 at S862 in your research applications.

How do I analyze contradictory results between GRIA4 phosphorylation levels and functional outcomes?

When faced with contradictory results between GRIA4 phosphorylation levels and functional outcomes, consider these analytical approaches:

• Temporal Dynamics: Phosphorylation states can be transient. Conduct time-course experiments to capture dynamic changes that might be missed at single time points.

• Regional Specificity: GRIA4 expression and phosphorylation patterns vary across brain regions. Ensure comparisons are made within the same anatomical structures.

• Cell-Type Heterogeneity: Different neuronal populations may exhibit distinct regulatory mechanisms. Consider using cell type-specific markers in co-localization studies to refine your analysis.

• Pathway Crosstalk: Multiple signaling pathways converge on GRIA4 regulation. Investigate whether compensatory mechanisms are activated in your experimental model.

• Methodological Considerations:

  • Antibody specificity issues can be addressed through multiple validation approaches

  • Quantitative limitations of Western blotting versus immunostaining should be considered

  • Functional assays may be influenced by factors beyond GRIA4 phosphorylation

• Statistical Analysis: Ensure appropriate statistical methods are applied, particularly when comparing multiple experimental conditions or time points.

What complementary techniques can validate Phospho-GRIA4 (S862) Antibody findings?

To strengthen the validity of findings obtained with Phospho-GRIA4 (S862) Antibody, consider implementing these complementary techniques:

• Phosphoproteomics: Mass spectrometry-based approaches can provide unbiased confirmation of phosphorylation at S862 and potentially identify additional phosphorylation sites.

• Site-Directed Mutagenesis: Generate S862A (phospho-dead) or S862D/E (phospho-mimetic) mutants to directly test the functional significance of phosphorylation at this site.

• Proximity Ligation Assay (PLA): This technique can confirm protein-protein interactions that are dependent on S862 phosphorylation status, such as PICK1 binding or calmodulin dissociation.

• Electrophysiology: Patch-clamp recordings can directly measure functional consequences of altered phosphorylation states, particularly when combined with phospho-mimetic mutations or pharmacological manipulations.

• Live Cell Imaging: Fluorescently tagged GRIA4 can be used to track trafficking dynamics in response to manipulations that alter S862 phosphorylation.

• Biochemical Fractionation: Subcellular fractionation can help quantify the distribution of phosphorylated GRIA4 between surface, endosomal, and intracellular compartments.

By combining these approaches with careful antibody-based detection, researchers can develop a more complete and reliable understanding of GRIA4 phosphorylation biology.

What are emerging areas of research involving GRIA4 phosphorylation at S862?

Several promising research directions are emerging in the study of GRIA4 phosphorylation at S862:

• Circuit-Specific Functions: Investigating how S862 phosphorylation differentially affects specific neural circuits could provide insights into region-specific synaptic plasticity mechanisms.

• Developmental Regulation: The temporal dynamics of GRIA4 phosphorylation during brain development remains poorly understood but could be critical for circuit formation and maturation.

• Disease Mechanisms: Exploring how pathogenic GRIA4 variants affect phosphorylation at S862 could reveal mechanisms underlying intellectual disability and seizure disorders associated with GRIA4 mutations .

• Therapeutic Targeting: Developing compounds that modulate S862 phosphorylation could offer therapeutic approaches for disorders characterized by glutamatergic dysfunction.

• Crosstalk with mGluR Signaling: Further investigation of the relationship between metabotropic glutamate receptors and GRIA4 phosphorylation could reveal new aspects of synaptic integration .

• Single-Cell Resolution Studies: Applying advanced imaging and single-cell analytical techniques could reveal cell type-specific regulation of GRIA4 phosphorylation that is masked in bulk tissue analyses.