SPG21 Human
Description
Introduction to SPG21 Human
SPG21 (spastic paraplegia 21) is an autosomal recessive gene located on chromosome 15q21-q22, encoding the protein maspardin (48 kDa). It is associated with Mast syndrome, a rare neurodegenerative disorder characterized by spastic paraparesis, cognitive decline, thin corpus callosum, and extrapyramidal symptoms . Maspardin belongs to the α/β hydrolase fold protein family and localizes to endosomal membranes, interacting with CD4 to modulate T-cell activation .
Key Features of SPG21
Genetic Mutations
SPG21 mutations typically cause truncation of maspardin, leading to loss of function. Reported mutations include:
Mast Syndrome
SPG21 mutations underlie complicated hereditary spastic paraplegia (HSP), with core features:
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Progressive spastic paraparesis (lower limb weakness, spasticity)
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Cognitive impairment (dementia, neuropsychiatric symptoms)
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MRI findings:
Case Study Data (Austrian/German Cohort):
Cellular Functions of Maspardin
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T-Cell Regulation:
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Endosomal Dynamics:
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Neuronal Development:
Circular RNA (circSPG21) in Intervertebral Disc Disease (IVDD)
Potential Therapeutic Targets
Challenges
Product Specs
Q&A
What is the SPG21 gene and its protein product maspardin?
SPG21 (also known as ACP33) is a gene mapping to chromosome 15q22.31 that encodes maspardin, a 308 amino acid cytoplasmic protein belonging to the AB hydrolase superfamily . The protein has a predicted molecular weight of approximately 34.8 kDa . Maspardin localizes primarily to endosomal/trans-Golgi network membranes and the cytoplasm, where it plays roles in protein transport and sorting . The name "maspardin" is derived from "Mast syndrome, spastic paraplegia, autosomal recessive with dementia," reflecting its involvement in this neurodegenerative condition .
Research methodology: To study maspardin at the molecular level, investigators typically use recombinant protein expression systems. Commercial recombinant maspardin is available with C-terminal tags (such as C-Myc/DDK) expressed in HEK293T cells, with purity typically >80% as determined by SDS-PAGE and Coomassie blue staining . For cellular studies, researchers can employ lentiviral particle systems containing maspardin shRNA to achieve knockdown of gene expression .
What are the clinical manifestations of Mast syndrome caused by SPG21 mutations?
Mast syndrome (SPG21) presents as a complicated form of hereditary spastic paraplegia (HSP) with the following clinical features:
What mutations in SPG21 cause Mast syndrome, and how are they distributed across populations?
Initially described in the Old Order Amish population where a founder mutation (601insA) causes a frameshift and premature termination (fs201-212X213) , SPG21 mutations have now been identified in multiple populations:
What neuroimaging findings are characteristic of SPG21 mutations?
Brain MRI in patients with Mast syndrome reveals distinctive features:
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Thin corpus callosum (notable finding)
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Global brain atrophy
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White matter abnormalities/demyelination
These imaging features suggest both developmental abnormalities (possibly explaining early subtle developmental issues) and ongoing neurodegeneration (explaining progressive symptoms) . The corpus callosum abnormality may represent partial agenesis, atrophy, or a combination of both .
Research methodology: Standard MRI protocols should include T1-weighted, T2-weighted, and FLAIR sequences to adequately visualize these features. Quantitative MRI techniques, including diffusion tensor imaging, can provide more detailed assessment of white matter tract integrity, which may be valuable for tracking disease progression .
What is known about maspardin's cellular localization and potential functions?
Maspardin colocalizes with CD4 on endosomal/trans-Golgi network membranes and is also found in the cytoplasm . Functional studies suggest multiple potential roles:
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Negative regulatory factor in CD4-dependent T-cell activation
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Involvement in protein transport and sorting in the endosomal/trans-Golgi network
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Interaction with the aldehyde dehydrogenase ALDH16A1
The protein's membership in the AB hydrolase superfamily suggests enzymatic activity, though specific substrates remain poorly characterized .
Research methodology: To investigate maspardin localization, immunofluorescence microscopy with co-staining for endosomal/Golgi markers is commonly employed. Protein interaction studies typically use co-immunoprecipitation, yeast two-hybrid assays, or proximity ligation assays to identify binding partners. For functional studies, knockdown approaches using shRNA in cell culture systems can reveal cellular consequences of maspardin deficiency .
How do clinical manifestations of SPG21 vary between populations with different mutations?
Phenotypic variations have been observed across different populations:
What methods are available for studying maspardin in experimental systems?
Several experimental approaches are available for maspardin research:
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Gene Knockdown/Knockout:
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Protein Expression and Purification:
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Functional Assays:
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CD4+ T-cell activation assays
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Vesicular trafficking assays
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Protein sorting assays
Research methodology: When conducting knockdown experiments, validation of knockdown efficiency by RT-qPCR and Western blotting is essential. For recombinant protein work, verification of protein integrity through SDS-PAGE, Western blotting, and activity assays ensures reliable results .
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How might maspardin dysfunction contribute to neurodegeneration?
Based on its cellular localization and function, several hypotheses may explain maspardin's role in neurodegeneration:
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Disruption of endosomal/trans-Golgi network protein sorting leading to accumulation of mislocalized proteins
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Impaired CD4-dependent signaling affecting neuroinflammatory processes
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Altered interaction with ALDH16A1 potentially affecting cellular detoxification pathways
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Disruption of membrane trafficking particularly affecting neurons with long axons (explaining the predominant corticospinal tract involvement)
Research methodology: Comparative studies between patient-derived and control cells (fibroblasts, lymphoblasts, or induced pluripotent stem cell-derived neurons) can reveal disrupted cellular processes. High-content imaging of vesicular trafficking, proteomic analysis of altered protein interactions, and transcriptomic profiling can identify dysregulated pathways .
What are the most effective experimental designs for identifying maspardin interaction partners?
To comprehensively identify maspardin interaction partners, a multi-method approach is recommended:
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Unbiased Screening Methods:
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Proximity-dependent biotin identification (BioID) to identify proteins in close proximity to maspardin
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Affinity purification followed by mass spectrometry (AP-MS)
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Yeast two-hybrid screening
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Validation Methods:
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Co-immunoprecipitation with endogenous proteins
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Fluorescence resonance energy transfer (FRET)
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Bimolecular fluorescence complementation (BiFC)
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Functional Validation:
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siRNA knockdown of candidate interactors
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Co-localization studies by super-resolution microscopy
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Competition binding assays
Research methodology: When using tagged recombinant maspardin for interaction studies, both N-terminal and C-terminal tagged versions should be tested, as tags may interfere with specific interactions. Controls should include proteins from the same cellular compartment that are not expected to interact with maspardin .
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How can patient-derived cellular models be developed to study SPG21 pathophysiology?
Patient-derived cellular models offer powerful tools for investigating disease mechanisms:
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Primary Cell Cultures:
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Skin fibroblasts from patients and controls
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Peripheral blood mononuclear cells for studying CD4+ T-cell function
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Reprogrammed Cells:
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Induced pluripotent stem cells (iPSCs) generated from patient fibroblasts
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iPSC differentiation into relevant cell types:
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Cortical neurons for studying cognitive aspects
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Motor neurons for studying spasticity
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Oligodendrocytes for studying white matter pathology
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Genome Editing Approaches:
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CRISPR/Cas9 correction of mutations in patient cells
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Introduction of patient mutations into wild-type cells to confirm causality
Research methodology: When establishing iPSC lines, multiple clones should be generated and characterized for pluripotency markers and genetic stability. Isogenic controls created through gene correction provide the most stringent comparison. Differentiation protocols should be optimized to achieve high purity of the target cell population .
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What considerations are important when developing therapeutic strategies for SPG21-related disorders?
Development of therapeutic approaches for Mast syndrome requires addressing several challenges:
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Gene Therapy Considerations:
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Selection of appropriate viral vectors that can cross the blood-brain barrier
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Design of compact expression cassettes (SPG21 cDNA is relatively small)
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Cell type-specific promoters for targeted expression
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Small Molecule Approaches:
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Identification of compounds that can modify protein trafficking/sorting
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Compounds that enhance alternative pathways compensating for maspardin loss
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Drug screening using patient-derived cellular models
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Biomarker Development:
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Identification of measurable indicators of disease progression
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Validation in natural history studies
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Correlation with clinical outcomes for use in clinical trials
Research methodology: Initial therapeutic screening can utilize patient-derived cellular models with high-content imaging of relevant cellular phenotypes. Promising candidates should be tested in appropriate animal models before clinical translation. Biomarker studies should include longitudinal assessment correlated with clinical measures .
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How does the pathophysiology of SPG21 relate to other forms of hereditary spastic paraplegia?
Comparing SPG21 with other HSP subtypes reveals important insights:
Product Science Overview
Mutations in the SPG21 gene cause Mast syndrome, an autosomal-recessive complicated form of hereditary spastic paraplegia . Mast syndrome is characterized by progressive weakness and spasticity of the lower limbs, dementia, thin corpus callosum, and white matter abnormalities . This neurodegenerative disorder leads to a slow, gradual decline in motor function, significantly impacting the quality of life of affected individuals.
The recombinant human SPG21 protein is produced using Escherichia coli (E. coli) expression systems . The protein is typically fused with a His-tag at the N-terminus to facilitate purification and detection . The recombinant protein is purified using conventional chromatography techniques to achieve high purity levels, often exceeding 95% .
Recombinant SPG21 protein is used in various research applications, including studies on T-cell activation and the molecular mechanisms underlying Mast syndrome . It serves as a valuable tool for understanding the pathophysiology of hereditary spastic paraplegia and for developing potential therapeutic interventions.
