SERPING1 Human
Description
Product Specs
Q&A
What is the SERPING1 gene and what does it encode?
SERPING1 (Serpin Family G Member 1) is a human gene that encodes C1 inhibitor (C1INH), a member of the serine protease inhibitor (serpin) superfamily. C1INH plays a critical role in regulating multiple biological pathways, including the complement, contact, coagulation, and fibrinolytic systems. Mutations in the SERPING1 gene are causally linked to Hereditary Angioedema (HAE), with reduced plasma levels of C1INH leading to enhanced activation of the contact system, triggering elevated bradykinin levels and increased vascular permeability . The importance of C1INH is underscored by its role as a crucial regulator of protease activity across multiple inflammatory and immune pathways .
What is the molecular structure of C1 inhibitor?
C1 inhibitor shares the highly conserved tertiary structure characteristic of serpins, consisting of:
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Three β-sheets (designated sA, sB, and sC)
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Eight to nine α-helices (termed hA-hI)
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A protruding reactive center loop (RCL)
The RCL forms a flexible stretch of approximately 20 amino acids outside the tertiary core, providing structural flexibility in a solvent-exposed environment. This region contains the scissile bond between positions P1 and P1′, which serves as a bait region for binding and cleavage by target proteases. When a protease cleaves this bond, the RCL undergoes a dramatic conformational change, inserting into the central sA β-sheet and dragging the covalently bound protease to the base of the serpin molecule, resulting in irreversible protease inhibition .
How is SERPING1 expressed in different cell types?
While hepatocytes are the primary source of C1 inhibitor production, research has identified other cellular sources of SERPING1 expression. The gene is expressed in hepatocytes and monocytes, with the latter potentially serving as a supplementary source of C1 inhibitor . Some contradictory data exist regarding SERPING1 mRNA levels across cell types, with Pappalardo et al. reporting decreased mRNA levels in certain scenarios, while Lappin et al. observed expression in monocytes . Recent research also suggests a role for SERPING1 in neuronal development, indicating expression in neural tissues during embryonic development .
What types of mutations occur in the SERPING1 gene?
SERPING1 can harbor a diverse range of pathogenic variants, including:
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Missense mutations (amino acid substitutions)
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Nonsense mutations (premature stop codons)
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Small insertions/deletions (leading to frameshift or in-frame alterations)
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Splice site mutations (affecting mRNA processing)
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Gross deletions or duplications (involving entire exons)
A study of Polish HAE patients identified 20 different types of sequence variants, with approximately half (9) being previously undescribed novel disease-associated variants. These included variants disrupting splice regions, nonsense mutations, and missense variants that impact C1INH protein structure and function . Specific examples from this study included gross duplications affecting exons 5 and 6, as well as gross deletions of exon 8 .
How do dominant-negative SERPING1 variants cause disease?
HAE type I patients typically show reduced plasma C1INH levels (20-30% of normal) despite being heterozygous for SERPING1 mutations. Research has revealed that some HAE-causing SERPING1 alleles exhibit dominant-negative effects on the wild-type protein. The mechanistic pathway involves:
Experimental studies showed that when normal C1INH was co-expressed with mutant variants, secretion of the normal protein was significantly reduced while intracellular accumulation increased. This phenomenon was observed across multiple HAE-causing variants, with the c.551_685del variant showing particularly severe effects .
How does SERPING1 genotype correlate with clinical phenotype in HAE?
The relationship between specific SERPING1 mutations and clinical phenotype demonstrates significant complexity. Studies of HAE patients reveal:
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Type I HAE is characterized by reduced plasma C1INH levels and is associated with various mutation types (missense, nonsense, deletions, etc.)
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Type II HAE shows normal or elevated but dysfunctional C1INH and is typically associated with specific mutations affecting the reactive center loop
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The severity of symptoms can vary even among patients carrying identical mutations
What cellular models are suitable for investigating SERPING1 function?
Researchers have successfully employed several cellular models for studying SERPING1:
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Hepatocyte-derived cell lines: HepG2 cells (human hepatocarcinoma) are particularly valuable for SERPING1 research as they represent the primary physiological source of C1INH production. These cells provide an appropriate environment for studying protein expression, secretion, and intracellular trafficking mechanisms .
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HeLa cells: While not natural producers of C1INH, these cells have been effectively used to study intracellular trafficking and protein-protein interactions involving C1INH variants. Their ease of transfection and imaging make them suitable for studying subcellular localization and ER stress responses .
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Primary cell cultures: Patient-derived fibroblasts have proved valuable for studying the effects of endogenous SERPING1 mutations, offering insights into disease mechanisms under physiological expression conditions .
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Neuronal models: For studying SERPING1's role in brain development, embryonic brain tissue and neuronal stem cells have been utilized, allowing for assessment of functions beyond complement regulation .
What methods are effective for tracking C1INH protein trafficking?
Several sophisticated approaches have been developed to monitor C1INH intracellular trafficking and secretion:
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Protein tagging strategies:
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HA-tagged C1INH constructs enable detection of both intracellular and secreted protein using anti-HA antibodies
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mCherry-fusion proteins allow for live-cell tracking and quantification of C1INH via fluorescence measurements
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Dual-labeling approaches (e.g., combining HA tags with fluorescent proteins) enable discrimination between normal and mutant proteins in co-expression studies
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Subcellular localization studies:
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Secretion analysis:
How can CRISPR/Cas9 be applied to SERPING1 research?
CRISPR/Cas9 technology has emerged as a powerful tool for SERPING1 research, enabling:
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Gene knockout studies: Complete elimination of SERPING1 expression allows assessment of its physiological functions in various cellular contexts. This approach was successfully employed to generate knockout embryos for studying SERPING1's role in neuronal stem cell proliferation during mouse embryonic brain development .
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Introduction of specific patient mutations: CRISPR-mediated homology-directed repair can introduce specific HAE-associated mutations to study their effects in isogenic cell lines, eliminating variables introduced by different genetic backgrounds.
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Correction of pathogenic variants: The technology can potentially restore normal SERPING1 function in patient-derived cells, allowing for proof-of-concept studies for gene therapy approaches.
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Regulatory element analysis: CRISPR interference or activation can be used to study the regulation of SERPING1 expression across different cell types .
What approaches can reveal non-complement functions of SERPING1/C1INH?
While C1INH is primarily known for its role in complement regulation, emerging research has uncovered additional functions:
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In utero electroporation: This technique allows for knockdown of SERPING1 in specific cell populations during embryonic development. Studies employing this approach revealed that SERPING1 affects neuronal stem cell proliferation and migration during mouse embryonic brain development .
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Sequential labeling experiments: By consecutively electroporating and labeling different cell populations, researchers have demonstrated that SERPING1 affects neuronal migration both cell-autonomously and non-cell-autonomously, influencing both genetically modified cells and neighboring cells .
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Proliferation assays: Incorporation of nucleotide analogs (e.g., IdU) during S phase, followed by immunostaining, can reveal SERPING1's effects on cell proliferation in developing tissues .
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Protein-protein interaction studies: Techniques such as co-immunoprecipitation, proximity ligation assays, and yeast two-hybrid screens can identify novel interaction partners for C1INH beyond complement components.
What are the optimal approaches for genotyping SERPING1 variants?
Comprehensive SERPING1 genotyping requires multiple complementary techniques:
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Sanger sequencing: The gold standard for identifying point mutations, small insertions, and deletions within the gene. This approach successfully identified 20 types of sequence variants in Polish HAE patients .
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Multiplex Ligation-dependent Probe Amplification (MLPA): Essential for detecting large deletions or duplications that may be missed by sequencing. This method identified gross duplications affecting exons 5 and 6, as well as gross deletions of exon 8 in HAE patients .
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Next-Generation Sequencing (NGS): Allows for high-throughput analysis of the entire gene, including intronic and regulatory regions, with increasing adoption in clinical and research settings.
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RNA analysis: Important for assessing the effects of variants on splicing and expression levels, particularly for deep intronic variants or when contradictory data exist regarding mRNA levels .
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In silico prediction tools: Software such as MutationTaster can help evaluate the potential pathogenicity of novel variants, though functional validation remains essential .
How can laboratory findings be correlated with SERPING1 variant pathogenicity?
Establishing causality for novel SERPING1 variants requires a multifaceted approach:
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Functional assays: Expressing the variant in cellular models to assess:
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Clinical laboratory parameters: Measuring:
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Family segregation analysis: Determining whether the variant co-segregates with disease in affected families
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Structural modeling: Predicting the impact of amino acid substitutions on protein folding, stability, and functional domains based on the known serpin structure
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Conservation analysis: Evaluating evolutionary conservation of affected residues across species and within the serpin superfamily
What is the current evidence regarding SERPING1 expression in non-hepatic cells?
The research on SERPING1 expression beyond hepatocytes reveals:
How do SERPING1 mutations induce ER stress responses?
The aggregation of mutant C1INH proteins within the endoplasmic reticulum triggers cellular stress responses:
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Structural alterations: HAE-causing SERPING1 variants lead to C1INH protein aggregation within the ER. The c.551_685del variant, in particular, demonstrates severe aggregation phenotypes with dramatic alterations to ER structure .
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ER morphology changes: Cells expressing mutant C1INH show a "constipated" ER structure that adapts to the shape of C1INH-HA foci, in contrast to the reticular-like structure observed in cells expressing normal C1INH .
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Unfolded protein response (UPR): The accumulation of misfolded C1INH likely activates the UPR, a cellular stress response that attempts to restore ER homeostasis or, if unsuccessful, triggers apoptosis.
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Serpinopathy mechanisms: The abnormal accumulation of C1INH in HAE type I connects this condition with other serpinopathies, suggesting shared pathogenic mechanisms despite different clinical manifestations .
What methodological approaches can distinguish cell-autonomous and non-cell-autonomous effects of SERPING1?
Sophisticated experimental designs have revealed dual mechanisms of SERPING1 action:
Product Science Overview
The SERPING1 gene is located on chromosome 11 and encodes a highly glycosylated plasma protein . The protein is synthesized in the liver and is involved in the regulation of the complement cascade by inhibiting activated C1r and C1s of the first complement component . This inhibition is essential for controlling the activation of the complement system, which is a part of the immune response.
The primary function of C1 Inhibitor is to form a proteolytically inactive stoichiometric complex with the C1r or C1s proteases . This action prevents the uncontrolled activation of the complement system, which could otherwise lead to tissue damage and inflammation. Additionally, C1 Inhibitor is a very efficient inhibitor of FXIIa, chymotrypsin, and kallikrein .
Deficiency or dysfunction of C1 Inhibitor is associated with a condition known as hereditary angioedema (HAE) . HAE is characterized by recurrent episodes of severe swelling (angioedema) in various parts of the body, including the extremities, face, gastrointestinal tract, and airway. This condition can be life-threatening if it leads to airway obstruction.
Human recombinant C1 Inhibitor is produced using recombinant DNA technology, which allows for the production of the protein in a controlled environment. This recombinant form is used therapeutically to treat patients with HAE by providing a functional C1 Inhibitor to regulate the complement system and prevent angioedema attacks.
Research on SERPING1 and its encoded protein continues to expand our understanding of its role in various physiological processes and its potential therapeutic applications. The recombinant form of C1 Inhibitor is also being explored for its use in other conditions where complement activation plays a role, such as certain autoimmune diseases and inflammatory conditions.
In summary, Serpin Peptidase Inhibitor, Clade G Member 1 (Human Recombinant) is a vital protein with significant roles in immune regulation and clinical applications, particularly in the treatment of hereditary angioedema.
