GO:0070080 titin Z domain binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0070080 titin Z domain binding is a molecular function describing the selective interaction between titin Z-repeat domains and the C-terminal calmodulin-like domain of alpha-actinin-2 (Act-EF34).
• This binding is a core structural event in Z-disc assembly, linking the giant sarcomeric protein titin to the actin-crosslinking protein alpha-actinin-2 at the Z-disc.
• The interaction is mediated by a helical region of the titin Z-repeat that inserts into a groove formed by the two helix pairs of Act-EF34.
• Titin Z-repeat binding to alpha-actinin-2 is essential for sarcomere cohesion and mechanosensing in striated muscle.
• Mutations or altered expression of Z-disc proteins such as ZASP, filamin C, and obscurin can disrupt titin Z-domain interactions and cause myofibrillar myopathies.
• CRISPR-based knockout, point-mutation, and knock-in models are powerful tools to dissect the causal role of titin Z-domain binding in muscle physiology and disease.
Description
GO:0070080 titin Z domain binding is a molecular function term that defines the specific binding of a titin Z protein domain to its target, the C-terminal calmodulin-like domain of alpha-actinin-2 (Act-EF34). Titin is a giant sarcomeric protein that spans from the Z-disc to the M-band and provides elasticity and structural integrity to muscle sarcomeres. The Z-disc is a highly organized structure where titin anchors to alpha-actinin-2, which in turn crosslinks actin filaments. The interaction between titin Z-repeats and alpha-actinin-2 is critical for Z-disc assembly and sarcomere cohesion. This binding event is not merely structural; it is also implicated in mechanosignaling and protein turnover at the Z-disc. Researchers study GO:0070080 to understand how mutations in Z-disc proteins lead to muscle diseases such as myofibrillar myopathies and cardiomyopathies. The term is also relevant for tissue engineering and regenerative medicine, where precise control of sarcomere assembly is desired. Understanding the molecular details of titin Z domain binding can inform the design of therapeutics targeting Z-disc dysfunction.
titin Z domain binding At A Glance
| GO ID | GO:0070080 |
|---|---|
| GO term | titin Z domain binding |
| Ontology | molecular_function |
| Synonym | Z repeat domain binding |
| Major function | Binding of titin Z-repeat domains to the C-terminal calmodulin-like domain of alpha-actinin-2 (Act-EF34), essential for Z-disc assembly and sarcomere cohesion. |
| Cellular location | Z-disc of striated muscle sarcomeres. |
| Key interacting partners | Alpha-actinin-2 (ACTN2), titin (TTN), and associated Z-disc proteins such as filamin C, ZASP, and obscurin. |
| Related disease | Myofibrillar myopathies, cardiomyopathies, and skeletal muscle disorders linked to Z-disc protein mutations. |
| Research methods | CRISPR knockout/knock-in, co-immunoprecipitation, surface plasmon resonance, X-ray crystallography, NMR, and live-cell imaging. |
What Is GO:0070080?
GO:0070080 titin Z domain binding is defined as the binding to a titin Z protein domain, which recognizes and binds to the C-terminal calmodulin-like domain of alpha-actinin-2 (Act-EF34), adopts a helical structure, and binds in a groove formed by the two planes between the helix pairs of Act-EF34. In simpler terms, it is the molecular function by which a specific repeated domain in titin (the Z-repeat) physically docks onto a complementary surface on alpha-actinin-2, thereby anchoring titin to the Z-disc.
Why Is titin Z domain binding Important in Cell Biology?
GO:0070080 titin Z domain binding is fundamentally important because it governs the assembly and mechanical stability of the Z-disc, a structure that transmits force in every heartbeat and muscle contraction. Disruption of this binding leads to sarcomere disorganization, muscle weakness, and disease. Moreover, the interaction serves as a paradigm for understanding how modular protein domains achieve high specificity in large multi-domain proteins. Studying this function provides insights into muscle development, mechanotransduction, and the molecular basis of myopathies.
• Essential for Z-disc assembly and sarcomere cohesion in cardiac and skeletal muscle.
• Mutations in titin or alpha-actinin-2 that impair this binding are linked to dilated cardiomyopathy and myofibrillar myopathies.
• Provides a structural model for how repeated domains (titin Z-repeats) recognize a single target surface (Act-EF34).
• Involved in mechanosignaling pathways that regulate muscle gene expression and protein turnover.
• Serves as a target for therapeutic strategies aiming to stabilize Z-discs in muscle disease.
• Key for understanding developmental processes such as myofibrillogenesis and sarcomere maturation.
• Relevant to tissue engineering of functional muscle constructs.
• Offers a paradigm for studying protein-protein interactions in large cytoskeletal complexes.
• Helps explain genotype-phenotype correlations in patients with Z-disc protein mutations.
• Enables the design of CRISPR-based models to test causality of specific mutations.
Molecular Mechanism of titin Z domain binding
Recognition of Act-EF34 by titin Z-repeats
In simple terms: Titin uses a repeated module to grab onto a specific pocket on alpha-actinin-2.
The titin Z-repeat domain adopts a helical structure that binds to a groove formed by the two helix pairs of the C-terminal calmodulin-like domain of alpha-actinin-2 (Act-EF34). This interaction is highly specific and is mediated by hydrophobic and electrostatic contacts. The binding is essential for anchoring titin to the Z-disc and for subsequent assembly of the sarcomere.
Structural basis of the interaction
In simple terms: The shape of the titin Z-repeat fits like a key into the lock of alpha-actinin-2.
Structural studies using NMR and X-ray crystallography have revealed that the titin Z-repeat forms an alpha-helix that inserts into a groove between the two helix pairs of Act-EF34. This binding mode is conserved among titin Z-repeats and is critical for high-affinity binding. The interaction surface involves residues that are mutated in some muscle diseases.
Role of cofactors and accessory proteins
In simple terms: Other Z-disc proteins help stabilize or regulate the titin-alpha-actinin connection.
Proteins such as filamin C, ZASP, and obscurin interact with titin or alpha-actinin-2 and modulate Z-disc assembly. For example, filamin C's actin-binding and titin-binding functions are distinct but both contribute to Z-disc cohesion. Obscurin regulates titin assembly at the Z-disk through interactions with Ran binding protein 9. These accessory proteins can affect the stability or dynamics of titin Z domain binding.
Regulation by alternative splicing and post-translational modifications
In simple terms: The cell can tune the strength of the connection by changing titin's message or adding chemical tags.
Titin is subject to extensive alternative splicing, which can include or exclude Z-repeats and thereby alter binding affinity to alpha-actinin-2. Post-translational modifications such as phosphorylation may also regulate the interaction, although specific sites remain to be fully mapped. These regulatory mechanisms allow muscle cells to adapt Z-disc structure to mechanical load.
Mechanical and signaling consequences
In simple terms: When titin binds alpha-actinin-2, it not only holds the sarcomere together but also sends signals.
The titin Z domain binding to alpha-actinin-2 is part of a mechanosensory complex that transmits force and initiates signaling cascades. Disruption of this binding leads to sarcomere instability and activation of stress responses. This function is therefore central to muscle homeostasis and disease.
Key Genes Involved in GO:0070080 titin Z domain binding
The following genes and proteins are directly or indirectly involved in GO:0070080 titin Z domain binding and its regulation in muscle cells.
| Gene | Major Role | Research Relevance |
|---|---|---|
| TTN | Encodes titin, the giant sarcomeric protein containing Z-repeats that bind alpha-actinin-2 | Mutations cause cardiomyopathies and myopathies; central to Z-disc assembly |
| ACTN2 | Encodes alpha-actinin-2, the actin-crosslinking protein whose C-terminal Act-EF34 domain binds titin Z-repeats | Mutations linked to cardiomyopathy and myofibrillar myopathy |
| FLNC | Encodes filamin C, an actin-binding protein that interacts with titin at the Z-disc | Mutations cause myofibrillar myopathy; regulates Z-disc cohesion |
| ZASP (LDB3) | Encodes ZASP, a PDZ-LIM protein that binds alpha-actinin and titin | Mutations in actin-binding domain disrupt actin filaments in myofibrillar myopathy |
| OBSCN | Encodes obscurin, a giant protein that regulates titin assembly at the Z-disk | Interacts with RanBP9; mutations linked to muscle disease |
| RANBP9 | Encodes Ran binding protein 9, which interacts with obscurin | Regulates titin assembly at Z-disk |
| Nesprin-2 (SYNE2) | Scaffold protein for telethonin and FHL-2 in the cardiomyocyte sarcomere | Links nuclear envelope to sarcomere; may influence Z-disc stability |
| Telethonin (TCAP) | Binds titin and nesprin-2 at the Z-disc | Mutations cause cardiomyopathy; part of Z-disc complex |
| FHL-2 | Four-and-a-half LIM domain protein that interacts with nesprin-2 and titin | Involved in sarcomere assembly and signaling |
| MYOZ2 | Myozenin-2, a Z-disc protein that binds alpha-actinin and titin | Mutations linked to cardiomyopathy; modulates calcineurin signaling |
| CSRP3 | Muscle LIM protein, interacts with alpha-actinin and titin | Mutations cause cardiomyopathy; role in mechanosensing |
| MYPN | Myopalladin, binds titin and alpha-actinin at Z-disc | Mutations linked to cardiomyopathy; regulates sarcomere assembly |
| ANKRD1 | Ankyrin repeat domain 1, interacts with titin and alpha-actinin | Mutations associated with cardiomyopathy; stress response |
| TCAP | Telethonin, binds titin Z-domain and nesprin-2 | Mutations cause limb-girdle muscular dystrophy and cardiomyopathy |
| TRIM63 | Muscle-specific E3 ubiquitin ligase that interacts with titin Z-domain | Regulates protein turnover at Z-disc; atrophy |
| FBXO32 | Atrogin-1, E3 ligase involved in muscle atrophy | May regulate titin Z-domain complex stability |
| CALM1 | Calmodulin, similar to Act-EF34 domain | Potential regulator of calcium-dependent interactions |
| CAPN3 | Calpain-3, protease that binds titin | Mutations cause limb-girdle muscular dystrophy; may cleave Z-disc proteins |
How Is titin Z domain binding Regulated?
The binding of titin Z-repeats to alpha-actinin-2 is regulated at multiple levels. Alternative splicing of TTN can include or exclude Z-repeat exons, thereby altering the number of binding sites and affinity for alpha-actinin-2. Post-translational modifications, such as phosphorylation by kinases like PKC or PKA, may modulate the interaction, although specific sites are still being mapped. Accessory proteins such as filamin C, ZASP, and obscurin can stabilize or compete for binding, influencing Z-disc assembly. Mechanical stretch can also trigger signaling cascades that remodel the Z-disc, involving calcium-dependent proteases like calpain-3. These regulatory mechanisms ensure that Z-disc structure adapts to mechanical demand and metabolic state.
titin Z domain binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| FLNC | Myofibrillar myopathy, cardiomyopathy | Knockout or point-mutation knock-in in C2C12 or iPSC-derived cardiomyocytes |
| ZASP (LDB3) | Myofibrillar myopathy with actin filament disruption | CRISPR knockout in skeletal muscle cells or mouse models |
| TTN | Dilated cardiomyopathy, tibial muscular dystrophy | Patient-derived iPSCs with titin mutations corrected by CRISPR |
| ACTN2 | Cardiomyopathy, myopathy | Knock-in of patient mutations in hiPSCs followed by cardiomyocyte differentiation |
| OBSCN | Muscle disease, cardiomyopathy | Knockout in zebrafish or mouse to study Z-disc assembly |
Myofibrillar myopathies
Mutations in Z-disc proteins that participate in titin Z domain binding, such as FLNC, ZASP, and ACTN2, cause myofibrillar myopathies characterized by sarcomere disorganization and muscle weakness. For example, ZASP mutations in the actin-binding domain disrupt skeletal muscle actin filaments and impair Z-disc integrity. Filamin C mutations that affect titin binding lead to Z-disc cohesion defects.
Cardiomyopathies
Altered titin Z domain binding is implicated in dilated cardiomyopathy and hypertrophic cardiomyopathy. Mutations in TTN, ACTN2, and other Z-disc genes can disrupt the interaction and lead to impaired cardiac contractility. Nesprin-2, which scaffolds telethonin and FHL-2, is also linked to cardiomyocyte sarcomere stability, and its dysfunction may contribute to cardiomyopathy.
Muscle atrophy and protein turnover
The Z-disc is a hub for protein quality control. E3 ubiquitin ligases such as TRIM63 and FBXO32 interact with titin Z-domain complexes and regulate their turnover. Dysregulation of these pathways contributes to muscle atrophy and cachexia, highlighting the importance of titin Z domain binding in muscle maintenance.
From titin Z domain binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of titin Z-repeat binding cause sarcomere disassembly? | CRISPR knockout of TTN Z-repeat exons in C2C12 myoblasts or hiPSCs |
| Do patient mutations in ACTN2 impair binding to titin? | Point-mutation knock-in of ACTN2 variants in hiPSCs followed by cardiomyocyte differentiation |
| Can a specific titin Z-repeat mutation be rescued by wild-type alpha-actinin-2? | Knock-in of tagged ACTN2 and live-cell imaging |
| What is the interactome of the titin Z-domain complex? | Overexpression of tagged titin Z-repeat followed by AP-MS |
| How does filamin C modulate Z-disc cohesion? | Knockout of FLNC in muscle cells and rescue with binding-deficient mutants |
| Does obscurin regulate titin assembly at the Z-disk? | Knockdown or knockout of OBSCN in cardiomyocytes |
How to Study the titin Z domain binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| NMR spectroscopy | Atomic-level structure and dynamics of titin Z-repeat/Act-EF34 complex | Determining binding interface and effects of mutations |
| X-ray crystallography | High-resolution structure of the complex | Visualizing helical binding groove |
| Surface plasmon resonance (SPR) | Binding affinity (KD) and kinetics | Comparing wild-type and mutant interactions |
| Co-immunoprecipitation (Co-IP) | In vivo protein-protein interactions | Validating titin-alpha-actinin-2 binding in muscle lysates |
| Fluorescence microscopy | Subcellular localization and sarcomere assembly | Assessing Z-disc integrity in knockout cells |
| CRISPR knockout screens | Identification of genes required for Z-disc cohesion | Discovering novel regulators of titin Z domain binding |
| Proteomics (AP-MS) | Interactome of titin Z-domain complex | Mapping dynamic protein networks |
| RNA-seq | Transcriptional changes upon disruption of binding | Identifying compensatory pathways |
Structural biology (NMR, X-ray crystallography)
High-resolution structures of titin Z-repeats bound to Act-EF34 have been solved using NMR and X-ray crystallography, revealing the helical binding mode and key contact residues. These methods are essential for understanding how mutations affect binding affinity and specificity.
Biophysical binding assays
Surface plasmon resonance (SPR), isothermal titration calorimetry (ITC), and pull-down assays are used to measure binding affinities between titin Z-repeats and alpha-actinin-2 variants. These quantitative methods help determine the impact of disease-associated mutations.
Cell imaging and sarcomere assembly
Fluorescence microscopy of tagged titin and alpha-actinin-2 in muscle cells allows visualization of Z-disc assembly and sarcomere organization. Live-cell imaging can track dynamics of the interaction during myofibrillogenesis.
CRISPR-based genetic screens
Genome-wide CRISPR knockout screens can identify modifiers of Z-disc integrity and titin Z domain binding. These screens are powerful for discovering novel regulators and disease modifiers.
How CRISPR Can Be Used to Study GO:0070080 titin Z domain binding
Knockout
CRISPR knockout of TTN Z-repeat exons or ACTN2 can abolish titin Z domain binding, leading to sarcomere disassembly and providing a clean model to study the function's necessity. Knockout of FLNC or ZASP similarly disrupts Z-disc cohesion and mimics myofibrillar myopathy phenotypes.
Point Mutation
Introducing patient-specific point mutations into ACTN2 or TTN via CRISPR base editing or HDR allows precise testing of how single amino acid changes affect binding affinity and sarcomere stability. Such models are invaluable for genotype-phenotype correlation.
Knock-in
Knock-in of tagged versions of titin or alpha-actinin-2 (e.g., GFP or HA) enables live-cell imaging and proteomic analysis of the Z-disc complex. Knock-in of disease mutations in hiPSCs followed by cardiomyocyte differentiation recapitulates human disease phenotypes.
Overexpression
Overexpression of wild-type or mutant titin Z-repeat domains can act as dominant-negative inhibitors of Z-disc assembly, revealing competitive interactions. Overexpression of alpha-actinin-2 mutants can also disrupt sarcomere structure and function.
How EDITGENE Supports titin Z domain binding Research
Researchers studying titin Z domain binding-related genes often need to determine whether a candidate gene is causally involved in Z-disc assembly, sarcomere cohesion, or muscle disease. EDITGENE provides a comprehensive suite of CRISPR services to create precisely engineered cell and animal models, enabling rigorous functional validation of genes and mutations identified in genomic or proteomic studies.
Contact EDITGENE today to design your custom CRISPR model for titin Z domain binding research.
Frequently Asked Questions About titin Z domain binding
What is GO:0070080 titin Z domain binding?
GO:0070080 is a molecular function term describing the binding of a titin Z protein domain to the C-terminal calmodulin-like domain of alpha-actinin-2 (Act-EF34), a key interaction for Z-disc assembly.
What genes are involved in titin Z domain binding?
Key genes include TTN (titin), ACTN2 (alpha-actinin-2), FLNC (filamin C), ZASP (LDB3), and OBSCN (obscurin), among others.
Why is titin Z domain binding important for muscle?
It anchors titin to the Z-disc and is essential for sarcomere cohesion, force transmission, and mechanosignaling in cardiac and skeletal muscle.
What diseases are linked to titin Z domain binding defects?
Mutations affecting this interaction are linked to myofibrillar myopathies, dilated cardiomyopathy, and other muscle disorders.
How can CRISPR be used to study titin Z domain binding?
CRISPR knockout, point mutation knock-in, and tagged knock-in models allow researchers to test the causal role of specific genes and mutations in Z-disc assembly and disease.
What is the structure of the titin Z-repeat bound to alpha-actinin-2?
The titin Z-repeat adopts a helical structure that binds in a groove formed by the two helix pairs of Act-EF34, as revealed by NMR and crystallography.
Which proteins interact with titin at the Z-disc?
Alpha-actinin-2, filamin C, ZASP, obscurin, telethonin, and nesprin-2 are among the key interacting proteins.
How is titin Z domain binding regulated?
It is regulated by alternative splicing of TTN, post-translational modifications, and accessory proteins such as filamin C and obscurin.
What methods are used to study titin Z domain binding?
Common methods include NMR, X-ray crystallography, SPR, co-immunoprecipitation, fluorescence microscopy, and CRISPR screens.
Can EDITGENE help create models for titin Z domain binding research?
Yes, EDITGENE provides knockout, point mutation, knock-in, overexpression, and CRISPR library screening services tailored to Z-disc and muscle disease research.
Conclusion
GO:0070080 titin Z domain binding is a fundamental molecular interaction that anchors titin to the Z-disc through alpha-actinin-2, ensuring sarcomere cohesion and mechanosignaling in muscle. Disruption of this binding by mutations or altered regulation contributes to myofibrillar myopathies and cardiomyopathies. Advanced CRISPR models and structural techniques continue to unravel the precise mechanisms and disease relevance of this interaction. Targeting titin Z domain binding may offer new therapeutic avenues for muscle disorders.
References
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- 3. Bowman AL et al.. 2008. The rho-guanine nucleotide exchange factor domain of obscurin regulates assembly of titin at the Z-disk through interactions with Ran binding protein 9.. Mol Biol Cell 19(9):3782-92 PMID: 18579686
- 4. Atkinson RA et al.. 2000. Binding of alpha-actinin to titin: implications for Z-disk assembly.. Biochemistry 39(18):5255-64 PMID: 10819994
- 5. Sorimachi H et al.. 1997. Tissue-specific expression and alpha-actinin binding properties of the Z-disc titin: implications for the nature of vertebrate Z-discs.. J Mol Biol 270(5):688-95 PMID: 9245597
- 6. Joseph C et al.. 2001. A structural characterization of the interactions between titin Z-repeats and the alpha-actinin C-terminal domain.. Biochemistry 40(16):4957-65 PMID: 11305911
- 7. Lin X et al.. 2014. Z-disc-associated, alternatively spliced, PDZ motif-containing protein (ZASP) mutations in the actin-binding domain cause disruption of skeletal muscle actin filaments in myofibrillar myopathy.. J Biol Chem 289(19):13615-26 PMID: 24668811
- 8. Kontrogianni-Konstantopoulos A et al.. 2005. Obscurin: a multitasking muscle giant.. J Muscle Res Cell Motil 26(6-8):419-26 PMID: 16625317
