JSRP1 Human

What is JSRP1 and where is it primarily expressed in humans?

JSRP1 (also known as JP-45) is an integral protein constituent of the skeletal muscle sarcoplasmic reticulum junctional face membrane. It has an apparent molecular mass of 45 kDa and plays a critical role in the functional expression of voltage-dependent Ca²⁺ channels . JSRP1 is specifically expressed in skeletal muscle tissue, where it forms part of the excitation-contraction coupling machinery. It interacts directly with Cav1.1 (the α1 subunit of the voltage-sensing dihydropyridine receptor, DHPR) and the luminal calcium-binding protein calsequestrin, positioning it as an important regulatory component in calcium homeostasis and muscle contraction .

What are the key structural features of the JSRP1 protein?

JSRP1 is a membrane protein with specific domains that enable its interactions with other components of the excitation-contraction coupling machinery. While the search results don't provide complete structural details, the protein is known to span the sarcoplasmic reticulum membrane and has binding domains that interact with both Cav1.1 in the transverse tubule membrane and calsequestrin within the sarcoplasmic reticulum lumen . This positioning makes JSRP1 a potential regulatory linker between voltage sensing at the cell surface and calcium release from intracellular stores, which is essential for muscle contraction .

What common variants of JSRP1 have been identified in the human population?

Two primary JSRP1 variants have been identified in the human population:

• c.323C>T (p.P108L) in exon 5

• c.449G>C (p.G150A) in exon 6

These polymorphisms occur naturally in the general population, but their frequency and distribution among different populations and in patients with neuromuscular diseases have not been comprehensively documented until recent studies began exploring their prevalence in specific groups such as the Swiss Malignant Hyperthermia population .

How does JSRP1 contribute to normal skeletal muscle excitation-contraction coupling?

JSRP1 plays a critical role in excitation-contraction (EC) coupling by modulating the sensitivity of the dihydropyridine receptor (DHPR). As an integral protein of the sarcoplasmic reticulum junctional face membrane, JSRP1 interacts with both Cav1.1 (the voltage-sensing component) and calsequestrin (a calcium-binding protein in the SR lumen) . This positioning allows JSRP1 to influence the coupling between membrane depolarization and calcium release from the sarcoplasmic reticulum, which is essential for muscle contraction. Studies suggest that JSRP1 affects the functional expression of voltage-dependent Ca²⁺ channels, thereby regulating calcium influx and subsequent calcium-induced calcium release from the sarcoplasmic reticulum .

What experimental evidence demonstrates the impact of JSRP1 variants on muscle function?

Research on JSRP1 variants has revealed significant effects on muscle function through various experimental approaches:

• Patch-clamp techniques have demonstrated that the presence of JSRP1 variants (P108L and G150A) decreases the sensitivity of the DHPR to activation .

• Studies in knockout mice models (JP45KO) have shown:

  • Loss of skeletal muscle strength

  • Alterations in excitation-contraction coupling

  • Age-related decline in sarcoplasmic reticulum Ca²⁺ release

• Cell culture experiments with heterologous expression systems have confirmed the direct interaction between JSRP1 and Cav1.1, and demonstrated how variants affect this interaction .

These experimental approaches collectively demonstrate that JSRP1 variants can significantly alter skeletal muscle function by modifying the sensitivity of the excitation-contraction coupling machinery.

What is the relationship between JSRP1 variants and malignant hyperthermia susceptibility?

The relationship between JSRP1 variants and malignant hyperthermia (MH) is complex. Studies in the Swiss MH population have investigated the frequencies of the two common JSRP1 polymorphisms (P108L and G150A) . Interestingly, these polymorphisms are equally distributed among malignant hyperthermia negative, equivocal, and susceptible individuals, suggesting they are not direct causative factors for MH .

How do researchers distinguish between pathological JSRP1 variants and benign polymorphisms?

Distinguishing between pathological JSRP1 variants and benign polymorphisms requires a multi-faceted approach:

• Functional studies: Researchers use patch-clamp techniques and calcium imaging to assess how variants affect DHPR sensitivity and calcium handling .

• Genetic epidemiology: Comparing the prevalence of variants in disease populations versus healthy controls helps determine if a variant is associated with disease. For example, studies have shown that common JSRP1 variants (P108L and G150A) are equally distributed among malignant hyperthermia negative, equivocal, and susceptible individuals, suggesting they may be modifiers rather than causative factors .

• Phenotypic correlation: Analyzing whether specific variants consistently associate with particular clinical presentations helps distinguish pathological from benign variants .

• In vitro expression systems: Heterologous expression of JSRP1 variants allows researchers to study their effects on protein-protein interactions and calcium channel function in controlled environments .

• Animal models: Knockout and knock-in models provide insights into physiological effects of JSRP1 alterations in vivo .

What novel JSRP1 fusion variants have been identified in cancer research?

A significant discovery in cancer research is the identification of a novel JSRP1 intergenic region–anaplastic lymphoma kinase (ALK) fusion in non-small cell lung cancer (NSCLC). This fusion, specifically a JSRP1 intergenic region–ALK fusion (Jintergenic: A20), was identified through next-generation sequencing in a female patient with stage IV B lung adenocarcinoma .

The fusion structure involves the JSRP1 intergenic region rearranged to exons 20–29 of ALK, retaining the intact ALK kinase domain. Simultaneously, exons 1–19 of ALK rearranged to exon 2 of LINC00211 (A19: LINC00211) . This non-reciprocal translocation creates a fusion product with kinase activity.

The significance of this discovery is that patients with this fusion responded favorably to alectinib (an ALK tyrosine kinase inhibitor), suggesting this novel fusion acts as a carcinogenic driver mutation that is targetable with existing therapies .

What techniques are most effective for studying JSRP1 function in skeletal muscle?

Research on JSRP1 function in skeletal muscle employs several sophisticated techniques:

• Patch-clamp techniques: These allow precise measurement of ion channel activity and have been instrumental in demonstrating how JSRP1 variants affect DHPR sensitivity to activation .

• DNA mutational analysis: Essential for identifying and characterizing JSRP1 variants in human populations and patient cohorts .

• Cell culture systems: Heterologous expression in cell lines allows controlled study of JSRP1 and its interactions with Cav1.1 and other proteins .

• Knockout mice models: JP45KO mice have provided valuable insights into the physiological roles of JSRP1 in muscle function and aging .

• Calcium imaging: Critical for measuring sarcoplasmic reticulum Ca²⁺ release and studying how JSRP1 affects excitation-contraction coupling .

• Protein-protein interaction assays: These help characterize the molecular interactions between JSRP1 and its binding partners in the excitation-contraction coupling machinery .

• Immunohistochemistry and fluorescence techniques: Used to localize JSRP1 within the complex architecture of skeletal muscle fibers .

How should researchers approach the study of JSRP1 fusion proteins in cancer?

Studying JSRP1 fusion proteins in cancer requires a comprehensive approach:

• Next-generation sequencing (NGS): NGS is crucial for identifying novel fusions like the JSRP1 intergenic region–ALK fusion. This approach can detect complex rearrangements at the DNA level .

• Confirmation with multiple techniques: To validate NGS findings and exclude discordance caused by transcriptional or post-transcriptional processes, researchers should employ:

  • Fluorescence in situ hybridization (FISH) to confirm gene rearrangements

  • Immunohistochemistry (IHC) to verify fusion protein expression

• Functional characterization: Investigating the biological function of fusion proteins through:

  • In vitro kinase assays

  • Cell transformation studies

  • Signaling pathway analyses

• Clinical correlation: Tracking patient responses to targeted therapies provides valuable insights into the pathogenic significance of novel fusions .

• Structural analysis: Determining how the fusion affects protein domains and activity can help predict therapeutic responses and resistance mechanisms .

The case of JSRP1 intergenic region–ALK fusion demonstrates the importance of this multi-modal approach, as validation with FISH and IHC confirmed the NGS findings, and clinical follow-up demonstrated the fusion's sensitivity to alectinib therapy .

How do researchers resolve contradictory data regarding JSRP1 function across different experimental models?

Resolving contradictory data in JSRP1 research requires systematic approaches:

• Model system considerations: Researchers must recognize that findings from different model systems (cell lines, primary cultures, animal models) may vary due to:

  • Species-specific differences in JSRP1 structure and function

  • Variations in expression levels between systems

  • Differences in the complement of interacting proteins present in each model

• Methodological standardization: Adopting consistent:

  • Experimental protocols

  • Measurement parameters

  • Data analysis techniques

• Integrative analysis: Combining data from multiple approaches:

  • Functional studies (patch-clamp, calcium imaging)

  • Structural analyses

  • Genetic association studies

  • Clinical observations

• Contextual interpretation: Considering results within the context of:

  • Developmental stage

  • Tissue specificity

  • Pathological conditions

  • Genetic background

• Direct comparative studies: Directly comparing JSRP1 function across different models under identical experimental conditions can help identify the source of contradictions .

What are the current technical limitations in studying JSRP1-protein interactions?

Several technical challenges complicate the study of JSRP1-protein interactions:

• Membrane protein complexities: As a membrane protein, JSRP1 presents inherent difficulties for:

  • Protein purification

  • Structural studies

  • Reconstitution experiments

• Dynamic interactions: The interactions between JSRP1 and partners like Cav1.1 and calsequestrin are likely dynamic and context-dependent, making them difficult to capture with static experimental approaches .

• Specialized cellular architecture: The triad junction where JSRP1 functions has a complex three-dimensional organization that is challenging to recreate in simplified experimental systems .

• Technological limitations:

  • Resolution limitations of current imaging techniques for visualizing protein-protein interactions in intact muscle

  • Challenges in developing specific antibodies for JSRP1 and its variants

  • Difficulties in maintaining physiological relevance in simplified systems

• Temporal aspects: The rapid kinetics of excitation-contraction coupling events makes it challenging to capture the temporal sequence of JSRP1 interactions during muscle activation .

Researchers are addressing these challenges through advances in cryo-electron microscopy, super-resolution imaging, and the development of more sophisticated muscle cell culture systems that better preserve the triad junction architecture .

What emerging methodologies might advance our understanding of JSRP1 function?

Several emerging methodologies hold promise for advancing JSRP1 research:

• CRISPR-Cas9 gene editing: Allows precise modification of JSRP1 to:

  • Create specific variants for functional studies

  • Develop improved cellular and animal models

  • Study the effects of JSRP1 alterations in human iPSC-derived muscle cells

• Advanced imaging techniques:

  • Super-resolution microscopy for visualizing JSRP1 within the triad junction

  • Live-cell calcium imaging with increased temporal and spatial resolution

  • Correlative light and electron microscopy to link JSRP1 localization with ultrastructural features

• Proteomic approaches:

  • Proximity labeling techniques (BioID, APEX) to identify JSRP1 interaction partners in intact cells

  • Cross-linking mass spectrometry to map interaction interfaces

  • Native mass spectrometry to study intact complexes containing JSRP1

• Single-cell analyses:

  • Single-cell transcriptomics to examine cell-specific expression patterns

  • Single-cell proteomics to study variability in JSRP1 abundance and modifications

  • Patch-seq approaches combining electrophysiology with transcriptomics

• Computational modeling:

  • Molecular dynamics simulations of JSRP1 interactions

  • Systems biology approaches to integrate JSRP1 into excitation-contraction coupling models

  • Structural predictions using AI-based tools like AlphaFold

How might understanding JSRP1 lead to novel therapeutic approaches for muscle disorders?

The growing understanding of JSRP1's role in muscle physiology suggests several potential therapeutic directions:

• Targeted modulation of JSRP1: Development of compounds that could:

  • Enhance JSRP1 function in conditions with decreased calcium sensitivity

  • Inhibit or modulate JSRP1 in conditions with calcium handling dysregulation

  • Stabilize JSRP1-Cav1.1 interactions in specific pathological contexts

• Genetic approaches:

  • Gene therapy to correct pathogenic JSRP1 variants

  • RNA-based therapeutics to modulate JSRP1 expression

  • Allele-specific approaches for dominant negative variants

• Personalized medicine strategies:

  • Pharmacogenomic approaches considering JSRP1 variants as modifiers of drug responses

  • JSRP1 genotyping to predict malignant hyperthermia risk and tailor anesthetic protocols

  • Therapeutic targeting based on individual JSRP1 variant profiles

• Combined targeting approaches:

  • Dual targeting of JSRP1 and RYR1 pathways in malignant hyperthermia

  • Complementary approaches addressing multiple aspects of calcium dysregulation

  • Lifestyle interventions combined with pharmacological approaches

The research on how JSRP1 variants can modify the phenotypic expression of RYR1 mutations in malignant hyperthermia provides a model for how genetic modifiers might be leveraged therapeutically in other muscle disorders with variable expressivity .