CHGB Human
Description
2.1. Regulation of Secretory Granule Biogenesis
CHGB plays a crucial role in the formation and maintenance of dense-core secretory granules in neuroendocrine cells. Studies have demonstrated that manipulating CHGB expression levels directly impacts granule morphology and abundance. When CHGB expression is silenced using siRNA in PC12 cells (a model for chromaffin cells), there is a significant approximately 48% reduction in the number of secretory granules, as observed by electron microscopy . Conversely, overexpression of CHGB through viral transduction results in approximately 122% greater abundance of secretory granules .
These findings highlight CHGB's essential function in the biogenesis pathway of secretory vesicles, particularly in catecholaminergic cells where these granules store and release neurotransmitters. The relationship between CHGB concentration and granule formation appears to be dose-dependent, with physiological levels being sufficient for normal granule development .
2.2. Chloride Channel Activity
One of CHGB's most remarkable functions is its ability to insert itself into membranes and form chloride-conducting channels. Unlike conventional ion channels with transmembrane domains, CHGB represents a novel class of chloride channels. Research has shown that CHGB interacts strongly with phospholipid membranes through two amphipathic α-helices .
At high local concentrations, CHGB insertion into membranes causes significant bilayer remodeling, producing protein-coated nanoparticles and nanotubules. Functional studies indicate that CHGB likely forms tetramers to create a channel with a single-channel conductance of approximately 125 pS (under conditions of 150/150 mM Cl⁻) . Notably, the CHGB channel exhibits higher anion selectivity than the six previously known families of Cl⁻ channels and is sensitive to anion channel blockers .
This chloride channel activity positions CHGB as an important factor in chloride homeostasis, which is crucial for various cellular functions including regulation of membrane potential, cell volume control, and endosomal/lysosomal function .
Distribution in Human Tissues
CHGB is primarily expressed in neuroendocrine tissues throughout the human body. The protein has been detected in:
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Pituitary gland - Specifically localized to epithelial cells, as demonstrated by immunohistochemical studies
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Adrenal medulla - Where it plays a crucial role in chromaffin granule formation
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Pancreatic islets - Contributing to hormone secretion regulation
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Neurons - Where it functions as a precursor for neuropeptides
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Various endocrine tumors - Including gastrinoma, thyroid carcinoma, insulinoma, pancreatic endocrine tumors, and pituitary adenomas
The distribution pattern of CHGB within cells is dimorphic, with both membrane-associated and soluble forms present. High-pressure freezing and immuno-electron microscopy techniques have confirmed this dual localization in secretory granules, particularly in pancreatic β-cells .
4.1. Neurological Disorders
Recent research has identified altered CHGB expression in several neurological conditions, most notably schizophrenia (SZ). Studies using induced neurons (iNs) derived from SZ patients have revealed dysregulation of CHGB neuropeptide secretion compared to control subjects. Specifically, lower numbers of distinct CHGB peptides were found in the secretion media from SZ neurons compared to controls .
This finding is consistent with reports of reduced chromogranin B levels in the cerebrospinal fluid and specific brain regions of schizophrenia patients. The iN neuronal model provides valuable insights into how CHGB dysregulation might contribute to the neurochemical imbalances observed in this condition .
4.2. Cardiovascular Implications
While Chromogranin A (CHGA) has been extensively studied for its role in blood pressure regulation, emerging evidence suggests that CHGB may have similar cardiovascular effects. In CHGB knockout mice, unregulated catecholamine release into plasma has been observed, which may contribute to elevated blood pressure .
The relationship between CHGB expression and cardiovascular function appears to involve multiple mechanisms:
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Regulation of catecholamine storage and release from chromaffin cells
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Formation of bioactive peptides that modulate vascular tone
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Potential feedback inhibition of sympathetic activity
These findings suggest that CHGB derangements may contribute to hypertension and other cardiovascular disorders, making it a potential target for therapeutic intervention .
4.3. Endocrine System Disorders
CHGB peptides have been identified in various endocrine tumors, including gastrinomas, thyroid carcinomas, insulinomas, pancreatic endocrine tumors, and pituitary adenomas . The presence of CHGB in these neoplasms suggests its potential utility as a biomarker for neuroendocrine tumors.
In pancreatic islets, CHGB channels on the cell surface appear to be important factors in the controlled batch-release of insulin-secretory granules . Dysregulation of this process could potentially contribute to disorders of glucose homeostasis, though more research is needed to fully elucidate these mechanisms.
5.1. Diagnostic and Prognostic Biomarkers
The tissue-specific expression pattern of CHGB makes it a promising biomarker for various conditions. Commercial ELISA kits have been developed for precise measurement of CHGB levels in human samples, including serum, plasma, and cell culture supernatants . These tools enable researchers and clinicians to quantify CHGB with high sensitivity and specificity.
The table below summarizes the key applications of CHGB measurement in clinical and research settings:
5.2. Therapeutic Potential
The multifunctional nature of CHGB makes it a compelling target for potential therapeutic interventions. Several approaches are being explored:
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Modulation of CHGB chloride channel activity to regulate cellular excitability and volume control
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Targeting CHGB-derived peptides to influence catecholamine release in hypertension
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Restoring normal CHGB expression in conditions where it is dysregulated, such as schizophrenia
The CHGB channel's unique structural and functional properties, distinct from other known chloride channels, make it a possible "druggable" target for future molecular therapeutics .
Product Specs
Q&A
What is the primary role of CHGB in human catecholamine storage?
CHGB serves as the major matrix protein in human catecholamine storage vesicles, playing a dual role in both intracellular and extracellular environments. Intracellularly, CHGB is critical for secretory granule biogenesis, determining both granule abundance and morphology. Research using siRNA in PC12 cells demonstrates that CHGB under-expression results in approximately 48% fewer secretory granules visible under electron microscopy . This protein participates in vesicular assembly at the trans-Golgi network and influences granule maturation through fusion, sorting, and membrane shedding processes .
Methodologically, researchers investigating CHGB's primary role should employ:
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Transmission electron microscopy for granule morphology assessment
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Quantitative PCR and Western blotting for expression analysis
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Cell fractionation techniques to isolate secretory vesicles
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Immunofluorescence microscopy with co-localization studies
How does CHGB genetic variation affect human physiology?
CHGB genetic variations significantly impact catecholamine secretion and blood pressure regulation. Two common CHGB promoter SNPs, A-296C (rs236140) and A-261T (rs236141), show strong association with hypertension in human populations . These genetic variations influence sympathoadrenal activity, an early etiological factor in hypertension development.
Research findings demonstrate:
| CHGB Genetic Variant | Physiological Effect | Clinical Association |
|---|---|---|
| Promoter SNP A-296C (rs236140) | Altered catecholamine secretion | Hypertension risk |
| Promoter SNP A-261T (rs236141) | Changed sympathoadrenal activity | Hypertension risk |
| CHGB knockout (animal model) | Elevated SBP and DBP | Hypertension |
For methodological validity, researchers should:
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Use genome-wide association studies with appropriate population stratification
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Employ haplotype analysis rather than single SNP studies
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Validate findings across multiple ethnic groups
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Correlate genotype with biochemical phenotypes (plasma catecholamines)
What experimental methods best evaluate CHGB effects on catecholamine dynamics?
Optimal evaluation of CHGB's impact on catecholamine dynamics requires a multi-faceted methodological approach. Research demonstrates that CHGB under-expression results in diminished capacity for catecholamine uptake (by ~79%) and a ~73% decline in stores available for nicotinic cholinergic-stimulated secretion .
Recommended experimental protocols include:
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Uptake studies:
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Radioisotope-labeled catecholamine uptake assays
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HPLC measurement of vesicular catecholamine content
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Kinetic analysis with varying substrate concentrations
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Release studies:
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Nicotinic cholinergic stimulation (specific pathway)
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Membrane depolarization protocols (non-specific pathway)
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Real-time amperometric measurements
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Fluorescent false neurotransmitter imaging
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When interpreting results, researchers should account for compensatory mechanisms, particularly CHGA over-expression observed when CHGB expression is diminished .
How can researchers effectively analyze CHGB knockout models?
CHGB knockout models provide critical insights into its physiological functions. Transmission electron microscopy of adrenal medulla in CHGB knockout mice reveals approximately 35% fewer granules (5.9±0.59 per μm² versus 9.1±0.55 per μm² in wild-type) and 44% smaller granule diameter (97.4±3.6 nm versus 173.1±6.3 nm) .
For comprehensive analysis, researchers should:
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Morphological assessment:
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Quantify granule number, size, and density using standardized protocols
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Assess granule ultrastructure with high-resolution EM techniques
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Compare multiple tissue types (adrenal medulla, sympathetic ganglia)
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Functional evaluation:
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Compensatory mechanism analysis:
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Evaluate expression changes in related proteins (especially CHGA)
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Compare acute (siRNA) versus chronic (genetic knockout) CHGB depletion
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Conduct rescue experiments with exogenous CHGB expression
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What mechanisms underlie CHGB's membrane insertion and chloride channel activity?
Recent research has established that CHGB not only functions as a matrix protein but also inserts into membranes to form a chloride-conducting channel. Fast kinetics and high cooperativity for anion efflux suggest that CHGB tetramerizes to form a functional channel with a single-channel conductance of approximately 125 pS under 150/150 mM Cl⁻ conditions .
Advanced methodological approaches to study this process include:
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Membrane insertion analysis:
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Channel activity characterization:
At high local concentrations, CHGB insertion in membranes causes significant bilayer remodeling, producing protein-coated nanoparticles and nanotubules . This property suggests a mechanistic role in secretory granule biogenesis beyond simple matrix functions.
How do CHGB proteolytic fragments regulate catecholamine secretion?
CHGB undergoes proteolytic processing to generate bioactive fragments that exert feedback inhibition on catecholamine secretion. Human CHGB protein and its proteolytic fragments inhibit nicotinic-stimulated catecholamine release by approximately 72%, with conserved-region peptides like hCHGB[60-67] specifically inhibiting nicotinic-triggered secretion by up to 41% .
This regulatory mechanism exhibits pathway specificity:
| Secretory Stimulus | Effect of CHGB Fragments | Mechanism |
|---|---|---|
| Nicotinic cholinergic | Inhibition up to 72% | Partial blockade of cationic signal transduction |
| Membrane depolarization | No inhibitory effect | Pathway-specific mechanism |
For methodological rigor, researchers should:
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Employ synthetic peptide screening across conserved CHGB regions
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Perform structure-activity relationship studies to identify active domains
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Investigate the chromaffin cell plasmin endoproteolytic system that generates these fragments in vivo
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Compare CHGB peptide effects with established inhibitors like CHGA-derived catestatin
How can researchers resolve contradictory findings on CHGB function between in vitro and in vivo models?
Reconciling contradictory data between experimental systems requires careful methodological considerations. Research shows that in CHGB knockout mice, plasma catecholamines increase (1.6-fold for norepinephrine, 1.7-fold for epinephrine), suggesting unregulated release . Conversely, in PC12 cells with CHGB silencing, there's a 73% decline in stores available for stimulated secretion .
Strategies to resolve these apparent discrepancies include:
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Methodological bridges:
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Primary cultures from knockout animals compared to cell lines
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Acute pharmacological inhibition versus chronic genetic deletion
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Temporal studies examining immediate versus compensated responses
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Comprehensive phenotyping:
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Compare granule morphology metrics across systems
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Evaluate both basal and stimulated catecholamine release
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Assess compensatory mechanisms, particularly CHGA upregulation
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Bidirectional manipulation:
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Study both over-expression and under-expression models
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CHGB over-expression yields 127% elevation in protein and 122% greater abundance of secretory granules, but only 14% increased catecholamine uptake
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This suggests a saturation effect where physiological CHGB levels are sufficient for optimal function
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What advanced imaging approaches best characterize CHGB-dependent secretory granule morphology?
High-resolution visualization of CHGB-dependent granule morphology requires sophisticated imaging techniques. Research demonstrates that CHGB knockout causes significant alterations in dense-core granule size and abundance .
State-of-the-art methodological approaches include:
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Ultrastructural analysis:
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Transmission electron microscopy with standardized quantification
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Immunogold labeling for protein localization
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Cryo-electron tomography for native state preservation
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Super-resolution fluorescence microscopy:
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STED (Stimulated Emission Depletion) for sub-diffraction imaging
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STORM/PALM for single-molecule localization
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Expansion microscopy for physical sample enlargement
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Dynamic visualization:
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Live-cell imaging with fluorescently-tagged CHGB
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Correlative light and electron microscopy (CLEM)
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Four-dimensional analysis (3D + time) of granule biogenesis
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These techniques enable quantitative assessment of granule parameters altered by CHGB manipulation:
| Parameter | Wild-type | CHGB Knockout | Change |
|---|---|---|---|
| Granule abundance | 9.1±0.55 per μm² | 5.9±0.59 per μm² | -35% |
| Granule diameter | 173.1±6.3 nm | 97.4±3.6 nm | -44% |
| Granule morphology | Dense core | Altered density | Qualitative |
How does CHGB interact with the broader chromogranin family in neuroendocrine regulation?
Understanding CHGB's role within the chromogranin family requires comparative functional analysis. Research suggests functional overlap between CHGB and CHGA, as both knockout models show unregulated catecholamine release and elevated blood pressure .
Methodological approaches to investigate these interactions include:
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Comparative expression analysis:
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Transcriptomic profiling across neuroendocrine tissues
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Co-regulation studies during physiological and pathological states
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Assessment of compensatory expression changes in single-knockout models
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Functional redundancy testing:
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Double-knockout models (CHGA/CHGB)
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Rescue experiments with heterologous expression
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Biochemical characterization of granule contents
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Interaction studies:
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Co-immunoprecipitation of chromogranin complexes
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FRET/BRET analysis of protein-protein interactions
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Native gel electrophoresis for complex formation
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Research shows specific compensation patterns, particularly CHGA mRNA over-expression when CHGB expression is diminished . This suggests evolutionary conservation of critical functions across the granin family, despite specialized roles for individual members.
What methodological considerations are critical when investigating CHGB's role in hypertension pathogenesis?
CHGB involvement in hypertension requires rigorous methodological approaches spanning molecular, cellular, and physiological analyses. Research has established that CHGB is over-expressed in rodent models of both genetic and acquired hypertension, suggesting augmented sympathoadrenal activity in these syndromes .
Critical methodological considerations include:
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Genetic association studies:
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Comprehensive SNP analysis beyond the two established variants (A-296C, A-261T)
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Haplotype determination across diverse populations
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Functional characterization of promoter variants using reporter assays
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Animal model validation:
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Comprehensive blood pressure phenotyping (ambulatory, stress-induced)
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Correlation with plasma and tissue catecholamine levels
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Pharmacological intervention studies targeting specific pathways
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Translational approaches:
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Biomarker development using CHGB fragments in human samples
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Correlation of genotype with therapy response
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Longitudinal studies of CHGB expression during hypertension development
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A mechanistic framework emerges wherein CHGB derangements lead to impaired catecholamine storage, elevated constitutive catecholamine release, and subsequent hypertension . This positions CHGB as both a potential biomarker and therapeutic target in catecholaminergic disease states.
Product Science Overview
Chromogranin B (CHGB) is a member of the granin family of proteins, which are acidic secretory proteins found in the secretory granules of neuroendocrine cells. These proteins play a crucial role in the regulated secretion of hormones and neurotransmitters. Human recombinant Chromogranin B is a synthetically produced version of this protein, used extensively in research to understand its functions and potential therapeutic applications.
The discovery of chromogranins dates back to the mid-20th century. In 1953, chromaffin granules were identified as co-storage sites for catecholamines and ATP . This discovery was soon followed by the identification of uniquely acidic proteins within these granules, leading to the classification of chromogranins. Chromogranin A (CgA) was the first to be identified, followed by Chromogranin B (CgB) and Secretogranin II (SgII) .
Chromogranin B is characterized by its acidic nature and the presence of numerous pairs of basic amino acids . It exists in both soluble and membrane-bound forms, making it dimorphic . This protein is critical for the formation of anion channels on the cell surface during regulated secretion . These channels are essential for maintaining ion homeostasis within secretory granules, which is necessary for the proper storage and release of hormones and neurotransmitters .
Chromogranin B plays a vital role in the neuroendocrine system. It is involved in the regulated secretion of hormones and neurotransmitters, which are crucial for various physiological processes. The protein’s ability to form anion channels helps maintain the ion balance within secretory granules, ensuring the proper functioning of neuroendocrine cells .
Human recombinant Chromogranin B is widely used in research to study its structure, function, and potential therapeutic applications. Recent studies have shown that Chromogranin B is critical for the appearance of robust anion conductances on the surface of neuroendocrine cells after regulated secretion . This makes it a potential target for therapeutic interventions in neurodegenerative diseases and other conditions related to ion homeostasis .
