GO:0035485 adenine/guanine mispair binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0035485 adenine/guanine mispair binding is a molecular function defined as binding to a double-stranded DNA region containing an A/G mispair.
• The A/G mispair is a non-Watson-Crick base pair that can arise from replication errors, oxidative damage, or spontaneous deamination, and its recognition is critical for genome stability.
• Metal alkali cations such as Na+ and K+ influence the hydrogen-bonding properties and tautomeric forms of the adenine-guanine mismatch, affecting its stability and recognition.
• Proteins involved in mismatch repair, such as MutS homologs, are the primary candidates for A/G mispair binding activity, though direct evidence for GO:0035485 remains limited.
• Defects in A/G mispair recognition are linked to cancer predisposition, particularly Lynch syndrome and other mismatch repair-deficient tumors.
• Experimental approaches to study GO:0035485 include electrophoretic mobility shift assays, surface plasmon resonance, and CRISPR-based knockout of candidate genes.
Description
The Gene Ontology (GO) term GO:0035485, adenine/guanine mispair binding, describes a molecular function in which a protein or complex binds to a double-stranded DNA region containing an adenine-guanine (A/G) mispair. This mispair is a non-Watson-Crick base pair that deviates from the canonical A-T and G-C pairs, and its presence in DNA can arise from replication errors, oxidative damage, or spontaneous deamination. The recognition of such mispairs is essential for maintaining genomic integrity, as failure to detect and repair them can lead to mutations and genomic instability. Researchers study GO:0035485 to understand the molecular mechanisms of DNA mismatch recognition and repair, which are fundamental to genome stability and cancer avoidance. The A/G mispair is one of several mismatches recognized by the mismatch repair (MMR) system, and its binding is a critical step in initiating repair. The physicochemical properties of the A/G mispair, including its hydrogen-bonding pattern and tautomeric forms, are influenced by the surrounding environment, such as the presence of metal alkali cations. Despite its importance, the specific proteins and structural determinants responsible for A/G mispair binding are not fully characterized, and the term remains a subject of active research. Understanding this function has implications for cancer biology, as defects in mismatch recognition are associated with hereditary and sporadic cancers. This article provides a comprehensive overview of GO:0035485, covering its definition, biological significance, key genes, research methods, and CRISPR-based models for studying it.
adenine/guanine mispair binding At A Glance
| GO ID | GO:0035485 |
|---|---|
| GO term | adenine/guanine mispair binding |
| Ontology | molecular_function |
| Synonym | A/G mispair binding, G/A mispair binding, guanine-adenine mispair binding |
| Definition | Binding to a double-stranded DNA region containing an A/G mispair. |
| Major function | Recognition of A/G mismatches in DNA for repair and genome maintenance. |
| Related process | DNA mismatch repair, DNA damage response. |
| Cellular location | Nucleus. |
| Influencing factors | Metal alkali cations (e.g., Na+, K+) affect hydrogen bonding and tautomeric forms of the A/G mispair. |
What Is GO:0035485?
GO:0035485 adenine/guanine mispair binding is defined as the binding to a double-stranded DNA region containing an A/G mispair. This molecular function involves the selective recognition of a non-complementary adenine-guanine base pair within the DNA double helix, distinguishing it from canonical Watson-Crick base pairs. The term is a child of DNA binding and is associated with processes such as DNA mismatch repair and DNA damage recognition.
Why Is adenine/guanine mispair binding Important in Cell Biology?
GO:0035485 is important because the recognition of A/G mispairs is a critical step in DNA mismatch repair, a pathway that safeguards genome stability and prevents mutations that can lead to cancer. Defects in mismatch recognition are associated with Lynch syndrome and other cancers, making this function a key area of study for understanding disease mechanisms and developing therapeutic strategies.
• A/G mispair binding is essential for initiating DNA mismatch repair, which corrects replication errors.
• Failure to recognize A/G mispairs leads to increased mutation rates and genomic instability.
• Defects in mismatch recognition are linked to hereditary cancer syndromes such as Lynch syndrome.
• The A/G mispair is a target for studying DNA-protein interactions and base-pair recognition mechanisms.
• Metal alkali cations modulate the stability and hydrogen bonding of the A/G mispair, influencing its recognition.
• Understanding A/G mispair binding can inform the design of drugs targeting mismatch repair-deficient tumors.
• Research on GO:0035485 contributes to basic knowledge of DNA repair pathways.
• CRISPR-based models enable functional dissection of genes involved in A/G mispair recognition.
Molecular Mechanism of adenine/guanine mispair binding
Recognition of the A/G Mispair
In simple terms: Proteins scan DNA and detect an A/G mismatch by its unusual shape and hydrogen-bonding pattern.
The A/G mispair is a non-Watson-Crick base pair that presents a distinct hydrogen-bonding pattern and helical distortion compared to canonical pairs. Proteins with A/G mispair binding activity, such as MutS homologs, recognize this distortion through specific amino acid residues that interact with the mismatch. The binding is thought to involve hydrogen bonds and stacking interactions that stabilize the protein-DNA complex.
Role of Metal Alkali Cations
In simple terms: Metal ions like sodium and potassium can change how the A/G mismatch behaves, affecting its recognition.
Metal alkali cations, including Na+ and K+, influence the hydrogen-bonding properties and tautomeric forms of the adenine-guanine mismatch. These cations can stabilize or destabilize specific tautomers, thereby modulating the binding affinity of proteins to the A/G mispair. The presence of such cations in the cellular environment may therefore regulate the efficiency of mismatch recognition.
Tautomeric Forms and Hydrogen Bonding
In simple terms: The A/G mismatch can exist in different chemical forms, and these forms affect how tightly proteins bind.
The A/G mispair can adopt various tautomeric forms, each with different hydrogen-bonding capabilities. Computational studies have shown that the relative stability of these tautomers is influenced by the surrounding environment, including metal cations. The specific tautomer recognized by repair proteins may determine the specificity and affinity of binding.
Structural Basis of Binding
In simple terms: The three-dimensional structure of the protein determines how it fits the A/G mismatch.
Structural studies of mismatch recognition proteins, such as MutS, have revealed conserved domains that interact with mismatched bases. For A/G mispair binding, the protein must accommodate the purine-purine mismatch without disrupting the overall DNA helix. The binding interface typically involves a conserved Phe or other aromatic residue that stacks against the mismatched base.
Downstream Signaling and Repair
In simple terms: Once a protein binds the A/G mismatch, it triggers a repair process.
Binding of a protein to the A/G mispair is the first step in mismatch repair, leading to recruitment of additional repair factors and excision of the mismatched region. This process ultimately restores the correct base pair and maintains genome integrity. Defects in this binding step can result in repair failure and mutation accumulation.
Key Genes Involved in GO:0035485 adenine/guanine mispair binding
The following genes encode proteins that are either directly implicated in A/G mispair binding or are key components of the mismatch repair pathway that recognizes this lesion.
| Gene | Major Role | Research Relevance |
|---|---|---|
| MSH2 | Core component of MutSα and MutSβ complexes that recognize DNA mismatches, including A/G mispairs. | Frequently mutated in Lynch syndrome; knockout models show microsatellite instability. |
| MSH6 | Partners with MSH2 to form MutSα, which binds to single-base mismatches and small loops. | Mutations linked to atypical Lynch syndrome; used in mismatch repair studies. |
| MSH3 | Partners with MSH2 to form MutSβ, which recognizes larger insertion-deletion loops. | May contribute to A/G mispair recognition in certain contexts. |
| MLH1 | Forms MutLα complex with PMS2, essential for downstream repair after mismatch binding. | Defects cause Lynch syndrome; used in functional assays. |
| PMS2 | Partners with MLH1 in MutLα, involved in excision and repair. | Mutations associated with Lynch syndrome; knockout models available. |
| PCNA | Sliding clamp that coordinates mismatch repair and interacts with MSH proteins. | Important for coupling recognition to repair; studied in vitro. |
| EXO1 | Exonuclease that excises the mismatched strand after recognition. | Functional studies in mismatch repair. |
| RPA | Single-stranded DNA-binding protein that stabilizes repair intermediates. | Supports mismatch repair progression. |
| DNA polymerase delta | Replicates DNA during repair synthesis. | Involved in final steps of mismatch repair. |
| DNA ligase I | Seals nicks after repair synthesis. | Completes mismatch repair. |
| MUTYH | Involved in base excision repair of oxidative damage, may crosstalk with mismatch repair. | Associated with colorectal cancer; potential A/G mispair relevance. |
| ATM | DNA damage response kinase that can be activated by mismatch repair intermediates. | Links mismatch recognition to cell cycle checkpoints. |
| ATR | DNA damage response kinase responding to replication stress. | May be activated by persistent A/G mispairs. |
| TP53 | Tumor suppressor that responds to DNA damage, including mismatch repair defects. | Frequently mutated in cancers with mismatch repair deficiency. |
| BRCA1 | DNA repair protein with roles in homologous recombination and mismatch repair crosstalk. | Potential modifier of mismatch repair defects. |
| BRCA2 | Homologous recombination repair protein. | May influence repair pathway choice after mismatch recognition. |
| POLH | Translesion synthesis polymerase that can bypass mismatches. | Potential backup pathway when mismatch repair fails. |
| REV1 | Translesion synthesis polymerase involved in bypassing DNA lesions. | May process A/G mispairs in repair-deficient cells. |
How Is adenine/guanine mispair binding Regulated?
The activity of A/G mispair binding is regulated at multiple levels. The expression of mismatch repair genes such as MSH2 and MSH6 is controlled by transcription factors including E2F and p53. Post-translational modifications, such as phosphorylation and ubiquitination, can modulate the stability and activity of MSH proteins. Additionally, the cellular levels of metal alkali cations, such as Na+ and K+, can influence the hydrogen bonding and tautomeric forms of the A/G mispair, thereby affecting binding affinity. The mismatch repair pathway is also regulated by the availability of ATP, which is required for MutS and MutL function.
adenine/guanine mispair binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MSH2 | Lynch syndrome, colorectal cancer | Knockout in HCT116 or RKO cell lines; point mutations in ATPase domain. |
| MLH1 | Lynch syndrome, endometrial cancer | Knockout in HeLa or HEK293; overexpression of mutant forms. |
| MSH6 | Atypical Lynch syndrome | Point mutation knock-in in mouse models; KO in cell lines. |
| PMS2 | Lynch syndrome, constitutional mismatch repair deficiency | Knockout in iPSCs; knock-in of patient mutations. |
| MUTYH | MUTYH-associated polyposis | Knockout in colorectal cell lines; overexpression studies. |
Lynch Syndrome and Hereditary Cancer
Lynch syndrome is an inherited condition caused by mutations in mismatch repair genes, particularly MSH2, MLH1, MSH6, and PMS2. Defects in A/G mispair binding, as part of mismatch recognition, lead to microsatellite instability and increased risk of colorectal, endometrial, and other cancers. The inability to recognize and repair A/G mispairs contributes to the mutator phenotype characteristic of Lynch syndrome tumors.
Sporadic Cancers with Mismatch Repair Deficiency
Beyond hereditary syndromes, sporadic tumors often exhibit mismatch repair deficiency due to epigenetic silencing of MLH1 or somatic mutations in MSH genes. These tumors share the mutator phenotype and may respond to immune checkpoint inhibitors, as mismatch repair deficiency generates neoantigens. A/G mispair binding activity is therefore a biomarker for mismatch repair status.
Therapeutic Implications
Cancers with defective A/G mispair recognition are sensitive to immune checkpoint blockade, such as anti-PD-1 antibodies. Understanding the molecular basis of A/G mispair binding can aid in developing targeted therapies that exploit mismatch repair defects. Additionally, drugs that modulate metal cation concentrations could potentially influence mismatch recognition and repair.
From adenine/guanine mispair binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does MSH2 directly bind A/G mispairs? | Recombinant MSH2-MSH6 complex in EMSA with A/G-containing oligonucleotides. |
| What is the effect of MSH2 knockout on A/G mispair recognition? | MSH2 knockout HCT116 cells; mismatch repair assays. |
| Can point mutations in MSH6 alter A/G binding affinity? | Knock-in of specific MSH6 mutations in HEK293 cells; SPR analysis. |
| Does overexpression of MSH3 enhance A/G mispair binding? | MSH3 overexpression in mismatch repair-deficient cells; immunoprecipitation. |
| What is the role of metal cations in A/G mispair binding? | In vitro binding assays with varying Na+ and K+ concentrations. |
| Can CRISPR screening identify novel A/G mispair binding proteins? | Genome-wide CRISPR knockout library in mismatch repair reporter cells. |
How to Study the adenine/guanine mispair binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| EMSA | Protein-DNA complex formation | Initial detection of A/G mispair binding by candidate proteins. |
| SPR | Binding kinetics (kon, koff, KD) | Quantitative comparison of wild-type and mutant proteins. |
| CRISPR knockout screen | Genes required for mismatch repair | Discovery of novel A/G mispair binding factors. |
| X-ray crystallography | 3D structure of protein-DNA complex | Atomic-level understanding of recognition. |
| Cryo-EM | 3D structure of large complexes | Structural analysis of MutS-MutL complexes on mispairs. |
| Isothermal titration calorimetry (ITC) | Binding affinity and thermodynamics | Characterization of cation effects on binding. |
| Fluorescence polarization | Binding affinity in solution | High-throughput screening of inhibitors. |
| Next-generation sequencing | Mutation load and microsatellite instability | Assessing functional consequences of repair defects. |
Electrophoretic Mobility Shift Assay (EMSA)
EMSA is used to detect protein-DNA complexes and can assess binding of proteins to A/G mispair-containing oligonucleotides. By comparing binding to A/G mispair versus canonical DNA, specificity can be determined. This method is straightforward and widely used for initial characterization.
Surface Plasmon Resonance (SPR)
SPR provides real-time kinetic measurements of binding affinity and specificity. It can quantify the interaction between purified proteins and immobilized A/G mispair DNA. SPR is valuable for studying the effects of mutations or cations on binding.
CRISPR-Cas9 Knockout Screening
Genome-wide CRISPR knockout screens can identify genes required for A/G mispair recognition and repair. Cells with a reporter for mismatch repair are transduced with a sgRNA library, and sgRNAs enriched in repair-deficient cells are identified. This approach can uncover novel components of the A/G mispair binding pathway.
Structural Biology (X-ray Crystallography and Cryo-EM)
Structural studies of mismatch repair proteins bound to A/G mispair DNA reveal the molecular basis of recognition. X-ray crystallography and cryo-EM can provide high-resolution details of the protein-DNA interface. These methods are essential for understanding how specific amino acids interact with the mispair.
How CRISPR Can Be Used to Study GO:0035485 adenine/guanine mispair binding
Knockout
CRISPR-Cas9 knockout of MSH2, MSH6, MLH1, or PMS2 in cell lines such as HCT116 or HEK293 abolishes A/G mispair binding and mismatch repair, leading to microsatellite instability. These knockout models are valuable for studying the consequences of loss of function and for testing compensatory pathways.
Point Mutation
Point mutations in the ATPase or DNA-binding domains of MSH2 or MSH6 can be introduced using CRISPR base editing or homology-directed repair. Such models allow dissection of specific residues required for A/G mispair binding without completely abolishing protein expression.
Knock-in
Knock-in of patient-derived mutations, such as those found in Lynch syndrome, into the endogenous locus of MSH2 or MLH1 provides physiologically relevant models. These can be used to study genotype-phenotype correlations and to test therapeutic interventions.
Overexpression
Overexpression of wild-type or mutant MSH2/MSH6 complexes using CRISPR activation or lentiviral vectors can enhance A/G mispair binding activity. This is useful for biochemical purification and for studying dominant-negative effects.
How EDITGENE Supports adenine/guanine mispair binding Research
Researchers studying adenine/guanine mispair binding-related genes often need to determine whether a candidate gene is causally involved in mismatch recognition, repair efficiency, or disease progression. EDITGENE provides a comprehensive suite of CRISPR-based services to enable such functional studies with high precision and reproducibility.
Contact EDITGENE today to design your custom CRISPR model for adenine/guanine mispair binding research.
Frequently Asked Questions About adenine/guanine mispair binding
What is GO:0035485 adenine/guanine mispair binding?
GO:0035485 is a Gene Ontology molecular function term defined as binding to a double-stranded DNA region containing an A/G mispair.
What genes are involved in adenine/guanine mispair binding?
Key genes include MSH2, MSH6, MSH3, MLH1, and PMS2, which encode components of the mismatch repair machinery that recognizes A/G mispairs.
How does the A/G mispair differ from normal base pairs?
The A/G mispair is a non-Watson-Crick purine-purine pair that causes helical distortion and is recognized by mismatch repair proteins.
What diseases are associated with defects in A/G mispair binding?
Defects are linked to Lynch syndrome and sporadic cancers with microsatellite instability, such as colorectal and endometrial cancers.
What methods are used to study A/G mispair binding?
Common methods include EMSA, SPR, CRISPR knockout screens, and structural biology techniques like X-ray crystallography.
How do metal cations affect A/G mispair binding?
Metal alkali cations such as Na+ and K+ influence the hydrogen-bonding properties and tautomeric forms of the A/G mispair, thereby affecting protein binding.
Can CRISPR be used to model A/G mispair binding defects?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models can be generated to study the function of genes involved in A/G mispair recognition.
What is the role of MSH2 in A/G mispair binding?
MSH2 forms a heterodimer with MSH6 (MutSα) that directly binds to A/G mispairs and initiates mismatch repair.
Is A/G mispair binding relevant to cancer therapy?
Yes, tumors with defective A/G mispair recognition often respond to immune checkpoint inhibitors, making this pathway a therapeutic target.
How can I study A/G mispair binding in my lab?
You can use biochemical assays like EMSA and SPR, or leverage CRISPR services from EDITGENE to create knockout or knock-in cell models.
Conclusion
GO:0035485 adenine/guanine mispair binding is a fundamental molecular function required for DNA mismatch repair and genome stability. Its dysregulation is directly linked to cancer predisposition and progression, making it a critical area of biomedical research. Advances in CRISPR-based models and biochemical assays continue to elucidate the mechanisms of A/G mispair recognition. EDITGENE provides comprehensive tools to study this function and its role in disease.
References
- 1. Shahi MR et al.. 2020. The effect of metal alkali cations on the properties of hydrogen bonds in tautomeric forms of adenine - Guanine mismatch.. J Mol Graph Model 100:107705 PMID: 32810731
