TSHB Human
Description
Overview of TSHB Human
TSHB Human refers to the recombinant beta subunit of thyroid-stimulating hormone (TSH), a glycoprotein hormone critical for regulating thyroid function. Produced in E. coli, this non-glycosylated polypeptide comprises 141 amino acids (residues 21–138) with a molecular mass of 15.9 kDa . It pairs with the alpha subunit (shared among glycoprotein hormones) to form active TSH, which stimulates thyroid hormone secretion.
| Property | Description |
|---|---|
| Amino Acid Sequence | 141 residues (21–138 a.a) |
| Molecular Weight | 15.9 kDa |
| Glycosylation Status | Non-glycosylated (produced in E. coli) |
| Source | Recombinant E. coli |
Role in TSH Hormone
TSHB Human constitutes the beta subunit of TSH, conferring biological specificity to the hormone. The alpha-beta dimer binds to the TSH receptor (TSHR) on thyroid follicular cells, triggering iodide uptake and hormone synthesis .
Gene Structure and Mutations
The TSHB gene (gene ID: 7252) spans 13 exons and encodes the beta subunit. Mutations disrupting the seatbelt region or altering subunit folding cause central congenital hypothyroidism (CCH), characterized by low TSH and thyroid hormone levels .
| Mutation Example | Phenotype | Reference |
|---|---|---|
| c.217A>C (novel variant) | Severe CCH, pituitary hyperplasia | |
| Deletions in seatbelt region | Loss of TSH bioactivity, hypoplastic thyroid |
Regulatory Mechanisms
-
TRH Stimulation: Binds to pituitary receptors, inducing TSHB transcription via Pit-1/GHF-1 (a pituitary-specific transcription factor) .
-
Thyroid Hormone Inhibition: T3/T4 suppress TSHB via thyroid hormone receptors, creating a negative feedback loop .
-
Photoperiodic Influence: Seasonal TSH expression in pars tuberalis thyrotropes (e.g., sheep, quails) is regulated by melatonin and transcription factors like Eya3 and Six1 .
Tissue-Specific Expression
Congenital Hypothyroidism
Mutations in TSHB account for ~1 in 65,000 cases of CCH, often missed in neonatal screening due to low TSH levels .
Autoimmune Thyroid Diseases
-
Graves’ Disease: TSHR-stimulating autoantibodies disrupt TSHR signaling.
-
Hashimoto’s Thyroiditis: Linked to TSHB mutations in rare cases .
Recombinant TSHB Human
Used in:
Diagnostic Tools
Product Specs
Thyroid-stimulating hormone beta (TSHB) is produced by thyrotrope cells in the anterior pituitary gland. It plays a crucial role in regulating the thyroid gland's production of thyroid hormones, namely triiodothyronine (T3) and thyroxine (T4). The hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates TSHB production and release. Conversely, somatostatin, also produced by the hypothalamus, inhibits TSHB release. A feedback loop exists where blood levels of T3 and T4 influence TSHB production. Low T3 and T4 levels stimulate TSHB production, while high levels suppress it.
TSHB
Q&A
What is the TSHB gene and what is its chromosomal location?
The human thyroid stimulating hormone β subunit (TSHB) gene is located on chromosome 1, specifically in the proximal portion of 1p22. This location has been determined through in situ hybridization and Southern blot analysis of human × mouse hybrid cells. The gene resides in a region that contains a conserved linkage group including amylase (AMY), nerve growth factor β subunit (NGFB), and NRAS, which are conserved between humans and rodents .
What is the functional significance of TSHB protein?
TSHB encodes the beta subunit of thyroid-stimulating hormone (TSH), a glycoprotein hormone essential for thyroid gland function. The beta subunit confers biological specificity, distinguishing TSH from other pituitary glycoprotein hormones that share a common alpha subunit. Bi-allelic loss-of-function mutations in TSHB cause congenital hypothyroidism, underscoring its critical role in thyroid hormone production and regulation .
How are TSHB variants typically identified in research settings?
Researchers employ several molecular techniques to identify TSHB variants:
-
Sanger sequencing remains the gold standard for detecting sequence variants
-
Restriction fragment length polymorphism (RFLP) analysis can be used for specific variants like R75G
-
For population studies, haplotype analysis using SNP arrays (such as Illumina Omni Express Beadchip) can identify shared homozygous loci
For the R75G variant specifically, researchers have designed primers (5'-AGAGGAGGGTCTCACTTTTGTC-3' – forward and 5'-ACCACTTAAGCTCTCTAACGCC-3' – reverse) with an annealing temperature of 62°C. The mutation creates a restriction site for NdeI, producing distinctive fragment patterns for wild-type and mutant alleles .
What is the significance of the TSHB R75G variant?
The TSHB R75G variant (previously referred to as R55G) represents a single nucleotide substitution (c.223A>G) resulting in the replacement of arginine with glycine at position 75 of the protein. Unlike pathogenic loss-of-function mutations, this variant does not impair TSH function but causes a structural change that prevents recognition by some monoclonal antibodies used in commercial TSH immune-detection platforms .
This structural alteration has significant clinical implications, as it can lead to:
-
Undetectable TSH in homozygotes using certain assays
-
Reduced TSH levels in heterozygotes
-
Erroneous diagnosis of hyperthyroidism or central hypothyroidism
How does the R75G variant impact different TSH detection methodologies?
The impact of the R75G variant on TSH detection varies significantly across different immunoassay platforms. The table below summarizes the detection capabilities of various FDA-approved immunoassays:
| Immunoassay Platform | Manufacturer | R75G Homozygote Detection | R75G Heterozygote Detection |
|---|---|---|---|
| ADVIA Centaur TSH3-UL | Siemens | No detection | Reduced levels |
| ADVIA Centaur TSH (2nd gen) | Siemens | No detection | Reduced levels |
| IMMULITE 2000 TSH | Siemens | No detection | Reduced levels |
| Architect TSH | Abbott Laboratories | Normal detection | Normal detection |
| COBAS-Roche MODULAR E170 | Roche Diagnostics | Normal detection | Normal detection |
This platform-dependent variability highlights the importance of methodological considerations in both research and clinical settings when working with populations where this variant may be prevalent .
What is the population distribution of the TSHB R75G variant?
The R75G TSHB variant has been reported to be prevalent in individuals of South Asian ethnicity, including populations from Pakistan and India. It has a minor allele frequency (MAF) of 0.012 for South Asians in the 1000 Genomes database, which is five-fold higher compared to the general population .
Notably, the variant has also been identified in the Bene Israel Indian Jewish population, suggesting a possible founder effect. Haplotype analysis using SNP arrays has been employed to examine the shared genetic background among affected individuals from geographically diverse but ancestrally related populations .
How can researchers distinguish between true TSH deficiency and detection artifacts?
Distinguishing between true TSH deficiency and detection artifacts due to variants like R75G requires a multi-platform approach:
-
Employ multiple immunoassay platforms with different epitope recognition properties
-
Include platforms known to detect variants of interest (e.g., Abbott Architect, Roche COBAS for R75G)
-
Measure free T4 (FT4) and free T3 (FT3) levels, which are typically normal in individuals with detection artifacts but abnormal in true TSH deficiency
-
Use serum dilution tests and heterophile antibody-blocking reagents to examine potential interference
What experimental approaches are effective for analyzing functional impacts of TSHB variants?
For comprehensive functional analysis of TSHB variants, researchers should consider the following methodological approaches:
-
In silico prediction: Utilize computational tools to predict the impact of amino acid substitutions on protein structure and function
-
Expression systems: Develop in vitro expression systems to assess protein production, stability, and secretion
-
Bioactivity assays: Measure the bioactivity of variant TSH using cell-based assays with thyroid stimulating hormone receptor expression
-
Structural analysis: Employ crystallography or molecular modeling techniques to understand structural perturbations
-
Epitope mapping: Use antibody panels with known epitope recognition sites to characterize variant effects on protein structure
-
Clinical correlation: Analyze thyroid function parameters in variant carriers to establish genotype-phenotype relationships
What are the current challenges in correlating TSHB genotypes with clinical phenotypes?
Several challenges exist in establishing clear TSHB genotype-phenotype correlations:
-
Assay variability: Different detection methods yield inconsistent results for variant carriers
-
Phenotypic complexity: Thyroid function is influenced by multiple genetic and environmental factors beyond TSHB
-
Variable expressivity: The same variant may manifest differently among carriers
-
Limited functional data: Many rare variants lack comprehensive functional characterization
-
Detection bias: Variants affecting TSH detection may lead to ascertainment bias in study populations
-
Population differences: Genetic background may influence the expression and impact of TSHB variants
To address these challenges, researchers should implement standardized phenotyping protocols across multiple assay platforms and integrate genetic, biochemical, and clinical data from well-characterized cohorts.
How does heterozygosity for the TSHB R75G variant affect thyroid function assessment?
This variability could potentially lead to misdiagnosis of subclinical hyperthyroidism in heterozygous carriers, highlighting the importance of considering genetic background when interpreting thyroid function tests. Researchers working with populations with high carrier rates should employ multiple assay platforms and consider genetic testing when unexpected thyroid function patterns emerge .
What research considerations are important when studying TSHB in diverse populations?
When designing research studies involving TSHB across diverse populations, several methodological considerations are crucial:
-
Population-specific variant frequencies: Screen for known population-specific variants like R75G in South Asian cohorts
-
Assay selection: Choose multiple assay platforms based on known detection capabilities for prevalent variants
-
Haplotype analysis: Consider haplotype backgrounds to identify potential founder effects
-
Clinical correlation: Correlate biochemical findings with clinical status to avoid misclassification
-
Genetic confirmation: Include genetic testing component, particularly in populations with known variant prevalence
-
Reference range adjustments: Consider whether population-specific reference ranges may be necessary for heterozygous carriers
These considerations help ensure that research findings accurately reflect biological reality rather than methodological artifacts.
Product Science Overview
The production of TSHB is controlled by Thyrotropin-Releasing Hormone (TRH), which is synthesized in the hypothalamus and transported to the anterior pituitary gland. TRH increases the production and release of TSHB. Conversely, somatostatin, also produced by the hypothalamus, inhibits the release of TSHB .
The levels of T3 and T4 in the blood create a regulatory negative feedback loop. When the levels of T3 and T4 are low, the production of TSHB is increased, and when the levels are high, the production is decreased .
Recombinant TSHB is produced using Escherichia coli (E. coli) as the host organism. The recombinant form is a single, non-glycosylated polypeptide chain containing 141 amino acids and has a molecular mass of 15.9 kDa. It is fused to a 23 amino acid His-tag at the N-terminus and purified using proprietary chromatographic techniques .
The recombinant TSHB is typically formulated as a sterile filtered clear solution containing 20 mM Tris-HCl buffer (pH 8.0), 0.4 M Urea, and 10% glycerol. It is recommended to store the solution at 4°C if it will be used within 2-4 weeks, or frozen at -20°C for longer periods. For long-term storage, adding a carrier protein such as 0.1% Human Serum Albumin (HSA) or Bovine Serum Albumin (BSA) is advised to prevent freeze-thaw cycles .
Recombinant TSHB is primarily used for laboratory research purposes. It is not intended for use as a drug, agricultural or pesticidal product, food additive, or household chemical. Researchers utilize recombinant TSHB to study thyroid function, hormone regulation, and related disorders such as hypothyroidism and Hashimoto’s thyroiditis .
The TSHB gene encodes the beta subunit of thyroid-stimulating hormone. This gene is part of a family of glycoprotein hormones that include chorionic gonadotropin (CG), luteinizing hormone (LH), and follicle-stimulating hormone (FSH). These hormones are dimers consisting of alpha and beta subunits that are associated non-covalently. The alpha subunits are identical across these hormones, but the beta chains are unique and confer biological specificity .
Mutations in the TSHB gene can lead to congenital central and secondary hypothyroidism and other thyroid-related disorders. The gene is located on chromosome 1 and has multiple transcript variants due to alternative splicing .
