STOML1 Human

What is STOML1 and how does it relate to other stomatin family proteins?

STOML1 (Stomatin-like protein 1) is a membrane protein belonging to the stomatin-domain family that in mammals includes five members: stomatin (STOM), stomatin-like proteins (STOML1, STOML2, STOML3), and podocin. All members share a conserved core domain called the stomatin-domain or SPFH (stomatin/prohibitin/flotillin/HflK/C) domain . STOML1 has a unique bipartite structure containing both a stomatin domain and a sterol carrier protein-2 (SCP-2) domain, distinguishing it from other family members . This structure suggests a specialized role in sterol/lipid transfer and transport not shared by other stomatin proteins . The protein is predominantly expressed in the brain, heart, and skeletal muscle, and at lower levels in other tissues including dorsal root ganglion (DRG) sensory neurons .

What are the alternative names and identifiers for STOML1?

Researchers should be aware of STOML1's multiple nomenclature to ensure comprehensive literature searches:

These alternative designations appear across different databases and publications, reflecting the protein's discovery history and functional relationships .

How is STOML1 expression distributed across different tissues?

STOML1 shows a specific tissue distribution pattern that differs from other stomatin family members. It is highly expressed in the brain and at significant levels in the heart and skeletal muscle . In neuronal tissues, STOML1 is expressed in dorsal root ganglion (DRG) sensory neurons, where it modulates the activity of acid-sensing ion channels (ASICs) . In the olfactory epithelium, STOML1 is expressed at very low levels compared to STOM and STOML3, with expression primarily limited to the cell bodies of mature olfactory sensory neurons (OSNs) and absent from the ciliary layer . This differential expression pattern suggests tissue-specific functions and possibly unique roles in different sensory systems .

What is the protein structure of human STOML1 and how does it differ from other stomatin family proteins?

Human STOML1 consists of 398 amino acids and has a distinctive bipartite structure that sets it apart from other stomatin family members. Its structure includes:

• A hydrophilic N-terminus containing a GYXXΦ sorting signal (where Φ represents a bulky, hydrophobic amino acid)

• A 30-residue hydrophobic domain that anchors the protein to the cytoplasmic side of membranes

• A stomatin/prohibitin/flotillin/HflK/C (SPFH) domain, also known as the prohibitin (PHB) domain

• A C-terminal sterol carrier protein-2 (SCP-2)/nonspecific lipid transfer protein domain

This unique combination of domains distinguishes STOML1 from other stomatin family proteins, none of which possess the SCP-2 domain . The presence of both stomatin and SCP-2 domains suggests STOML1's specialized function in lipid/sterol transfer and transport, particularly between membrane compartments . The protein's insertion into the membrane occurs through the short hydrophobic hairpin located at the N-terminus .

What is the subcellular localization of STOML1 and how is it targeted?

STOML1 exhibits a distinct subcellular localization pattern:

• It localizes primarily to late endosomal compartments

• Unlike stomatin, STOML1 is not found at the plasma membrane under normal conditions

• The targeting to late endosomes is mediated by a GYXXΦ sorting signal at the N-terminus

• Mutation of this signal results in plasma membrane mislocalization

In olfactory sensory neurons, STOML1 localizes mainly to the cell body and is absent from the ciliary layer, where odorant reception occurs . In dorsal root ganglion neurons, STOML1 co-localizes with and modulates acid-sensing ion channels (ASICs) . The protein associates with detergent-resistant membranes, suggesting localization to specialized membrane microdomains . This specific subcellular distribution pattern is crucial for its proper function in cholesterol/lipid trafficking and ion channel modulation .

How does STOML1 interact with membrane microdomains?

STOML1 associates with detergent-resistant membranes (DRMs), suggesting its incorporation into specialized membrane microdomains or "lipid rafts" . This association likely relates to STOML1's function in cholesterol trafficking and membrane organization. Within late endosomes, STOML1's interaction with membrane domains is functionally significant:

• The protein's stomatin domain may facilitate protein-protein interactions and oligomerization within these microdomains

• The SCP-2 domain likely mediates interaction with cholesterol and other lipids

• Through these domain-specific functions, STOML1 can coordinate cholesterol transfer between membrane compartments

Under conditions of blocked cholesterol efflux from late endosomes, overexpression of STOML1 induces the formation of enlarged, cholesterol-filled, weakly LAMP-2-positive acidic vesicles in the perinuclear region . This massive cholesterol accumulation depends specifically on the SCP-2 domain, confirming its role in cholesterol transfer to late endosomes . These findings indicate that STOML1's interaction with membrane microdomains is integral to its function in cellular cholesterol homeostasis.

What is the functional relationship between STOML1 and stomatin?

STOML1 and stomatin exhibit a complex functional relationship characterized by direct interaction and mutual influence on subcellular localization:

• STOML1 and stomatin co-localize in the late endosomal compartment

• The proteins co-immunoprecipitate, demonstrating direct physical interaction

• Both associate with detergent-resistant membranes

• Overexpression of STOML1 leads to redistribution of stomatin from the plasma membrane to late endosomes

This relationship mirrors that observed between their orthologues in C. elegans, where UNC-24 (STOML1 orthologue) controls the distribution and stability of UNC-1 (stomatin orthologue) . The interaction between these proteins may be crucial for their functions in regulating ion channel activities in neuronal and muscle tissues . The redistribution effect suggests STOML1 may serve as a regulator of stomatin trafficking and consequently influence stomatin-dependent processes at the plasma membrane.

How does STOML1 influence cholesterol transport and homeostasis?

STOML1's role in cholesterol transport and homeostasis stems from its unique domain structure, particularly the C-terminal sterol carrier protein-2 (SCP-2) domain. Research indicates several key mechanisms:

• STOML1 may facilitate cholesterol transfer to late endosomes

• Under conditions of blocked cholesterol efflux, STOML1 overexpression induces the formation of enlarged, cholesterol-filled vesicles

• This cholesterol accumulation strictly depends on the SCP-2 domain

• The localization of STOML1 to late endosomes positions it strategically for intracellular cholesterol trafficking

What is the role of STOML1 in modulating ion channel function?

STOML1 modulates several ion channels, particularly acid-sensing ion channels (ASICs), with specific effects:

• It can specifically inhibit proton-gated current of ASIC1 isoform 1

• It increases the inactivation speed of ASIC3

• It may be involved in regulation of proton sensing in dorsal root ganglion neurons

These modulatory effects on ion channels may explain STOML1's role in neuronal function, particularly in sensory systems. The interaction with ASICs suggests STOML1 may influence pain sensation, mechanoreception, and other sensory modalities dependent on these channels . Additionally, the protein's ability to regulate cholesterol distribution could indirectly affect the function of multiple ion channels and receptors that depend on membrane cholesterol for proper activity. This dual mechanism—direct interaction with ion channels and regulation of membrane cholesterol—may underlie STOML1's physiological importance in sensory neurons.

What methods are effective for detecting and analyzing STOML1 expression?

Researchers studying STOML1 can employ several complementary techniques for detection and analysis:

Nucleic Acid-Based Methods:

• RT-PCR for basic expression detection (as demonstrated in olfactory epithelium studies)

• qRT-PCR for quantitative comparison across tissues

• RNA sequencing for comprehensive transcriptomic analysis

Protein Detection Methods:

• Western blotting (WB) using recombinant STOML1 as a positive control

• Immunohistochemistry and immunofluorescence for tissue localization

• Co-immunoprecipitation for protein-protein interaction studies

Recombinant Systems:

• Wheat germ expression systems have been successfully used to produce full-length (1-398 aa) recombinant human STOML1 for ELISA and WB applications

When designing experiments, researchers should consider STOML1's variable expression levels across tissues and the specificity of antibodies to avoid cross-reactivity with other stomatin family members. Using genetic knockout models (as in STOML3 KO and Triple KO mice) can provide excellent specificity controls for antibody-based detection .

What are the best experimental models for studying STOML1 function?

Several experimental models have proven valuable for investigating STOML1 function:

Cellular Models:

• Overexpression systems in mammalian cell lines to study subcellular localization and cholesterol transport

• Knockdown/knockout cell lines using RNAi or CRISPR-Cas9 to study loss-of-function effects

• Primary neuronal cultures from relevant tissues (brain, DRG, olfactory neurons) for physiological studies

Animal Models:

• Mouse models with genetic manipulation of STOML1 and related proteins

• The Triple KO mouse (lacking STOM, STOML1, and STOML3) provides a complete background to study reconstituted expression

• C. elegans with mutations in the STOML1 orthologue UNC-24 for evolutionary conserved functions

Functional Assays:

• Electrophysiological recordings to assess ion channel modulation

• Cholesterol transport assays using fluorescent cholesterol analogs

• Membrane microdomain isolation through detergent-resistant membrane preparation

The choice of model should align with the specific STOML1 function being investigated, with neuronal systems being particularly relevant for studying its role in sensory function and ion channel modulation.

How can researchers effectively study STOML1 interactions with other proteins?

To study STOML1's protein-protein interactions, researchers can employ multiple complementary approaches:

Co-immunoprecipitation (Co-IP):

• Has successfully demonstrated direct interaction between STOML1 and stomatin

• Can be performed in both overexpression systems and native tissues

• Requires specific antibodies or epitope tagging

Proximity Labeling Techniques:

• BioID or APEX2-based approaches to identify proteins in close proximity to STOML1

• Particularly useful for identifying transient or weak interactions

Microscopy-Based Methods:

• Co-localization studies using immunofluorescence

• Förster resonance energy transfer (FRET) for direct protein interactions

• Fluorescence recovery after photobleaching (FRAP) to study dynamic interactions

Functional Assays:

• Electrophysiological recording of ion channels in the presence/absence of STOML1

• Cholesterol transport assays to study lipid transfer function

• Mutational analysis of specific domains (stomatin domain vs. SCP-2 domain)

When designing interaction studies, researchers should consider the membrane-associated nature of STOML1 and its localization to specific subcellular compartments. Domain-specific mutations can help distinguish interactions mediated by the stomatin domain versus the SCP-2 domain .

How does STOML1 contribute to neuronal function in sensory systems?

STOML1's role in sensory neuronal function appears multifaceted and system-specific:

In Dorsal Root Ganglion (DRG) Neurons:

• Modulates acid-sensing ion channels (ASICs) by:

  • Specifically inhibiting proton-gated current of ASIC1 isoform 1

  • Increasing inactivation speed of ASIC3

• May regulate proton sensing, potentially influencing pain perception and mechanosensation

In Olfactory Sensory Neurons (OSNs):

• Expressed at low levels primarily in cell bodies of mature OSNs

• Absent from the ciliary layer where odorant reception occurs

• Expression pattern differs from STOM and STOML3, which are more abundant in OSNs

The differential expression pattern suggests distinct roles across sensory systems. STOML1's conserved function may relate to its evolutionary relationship with C. elegans UNC-24, which is essential for touch sensitivity when interacting with MEC-2 . The protein likely contributes to sensory neuronal function through both direct ion channel modulation and indirect effects on membrane organization via cholesterol trafficking. Future research should explore how STOML1's dual domain structure enables it to coordinate these functions in specific sensory contexts.

What is the significance of STOML1's unique bipartite domain structure and how does it influence protein function?

STOML1's bipartite structure containing both a stomatin domain and a sterol carrier protein-2 (SCP-2) domain is unique among stomatin family proteins and critical to its function:

Functional Implications of Domain Structure:

• The stomatin domain likely mediates:

  • Protein-protein interactions, particularly with other stomatin family members

  • Association with membrane microdomains

  • Oligomerization and complex formation

• The SCP-2 domain is responsible for:

  • Cholesterol binding and transfer capabilities

  • Formation of enlarged cholesterol-filled vesicles when overexpressed

  • Directional transport of cholesterol to late endosomes

This unique domain combination enables STOML1 to serve as a functional bridge between membrane organization/protein interactions (via the stomatin domain) and lipid/sterol trafficking (via the SCP-2 domain). Experimental evidence demonstrates that cholesterol accumulation in late endosomes depends specifically on the SCP-2 domain . The evolutionary conservation of this bipartite structure from C. elegans to humans suggests its fundamental importance in cellular physiology, particularly in tissues with specialized membrane organization requirements such as the nervous system.

How does STOML1 function compare between different species and what evolutionary insights can be gained?

Comparative analysis of STOML1 across species reveals important evolutionary insights:

Evolutionary Conservation:

• The unique bipartite structure (stomatin + SCP-2 domains) is conserved from C. elegans (UNC-24) to humans (STOML1)

• This structural conservation suggests fundamental functional importance

Functional Comparison:

• In C. elegans, UNC-24 (STOML1 orthologue) controls the distribution and stability of UNC-1 (stomatin orthologue)

• Similarly, human STOML1 influences stomatin distribution when overexpressed

• C. elegans UNC-24 co-localizes and interacts with MEC-2 and is essential for touch sensitivity

• This evolutionary conservation of interaction patterns suggests conserved sensory functions

Species-Specific Adaptations:

• The number of stomatin family members varies across species (humans have 5, while C. elegans has 10)

• This expansion/contraction may reflect adaptation to species-specific requirements

• Expression patterns and tissue distribution may vary across species, potentially reflecting functional specialization

Understanding these evolutionary relationships provides context for interpreting human STOML1 function and may guide experimental approaches. The conserved interaction between STOML1/UNC-24 and stomatin/UNC-1 across diverse species highlights the fundamental importance of this protein-protein interaction in cellular physiology, particularly in neuronal function .

What pathological conditions might be associated with STOML1 dysfunction?

While direct evidence linking STOML1 to specific human diseases remains limited, its molecular functions suggest potential involvement in several pathological conditions:

Neurological Disorders:

• Given STOML1's high expression in the brain and role in sensory neuronal function, dysfunction could contribute to:

  • Sensory processing disorders

  • Neuropathic pain conditions (through ASIC channel modulation)

  • Neurodegenerative diseases involving cholesterol metabolism dysregulation

Lipid Metabolism Disorders:

• STOML1's role in cholesterol transport suggests potential involvement in:

  • Disorders of intracellular cholesterol trafficking

  • Lysosomal storage diseases

  • Conditions involving late endosomal dysfunction

Cancer Biology:

• The finding that STOML1 may protect FBXW7 isoform 3 from degradation suggests potential implications in:

  • Cancer progression, as FBXW7 is a recognized tumor suppressor

  • Cell cycle regulation

  • Therapeutic resistance

Research exploring these potential pathological connections remains in early stages. Future studies should investigate STOML1 expression and function in disease models and patient samples to establish clearer links between STOML1 dysfunction and specific pathological conditions.

What are the challenges in generating and using antibodies against STOML1?

Researchers face several challenges when developing and utilizing antibodies for STOML1 detection:

Specificity Issues:

• The stomatin domain is highly conserved across family members, risking cross-reactivity

• Antibodies must be validated against multiple stomatin family proteins

• Knockout models provide essential negative controls for specificity testing

Epitope Accessibility:

• STOML1's membrane association may mask certain epitopes

• Fixation and permeabilization methods can affect epitope detection

• Different experimental applications (WB, IHC, IP) may require different antibody clones

Validation Approaches:

• Use recombinant human STOML1 protein as a positive control

• Test against STOML1 knockout tissues/cells as negative controls

• Compare subcellular localization patterns with published reports

• Verify results with multiple antibodies targeting different epitopes

How can researchers effectively design experiments to distinguish between STOML1's various proposed functions?

To dissect STOML1's multiple proposed functions, researchers should employ domain-specific and context-dependent experimental designs:

Domain-Specific Approaches:

• Generate constructs with mutations in specific domains:

  • Stomatin domain mutants to assess protein-protein interactions

  • SCP-2 domain mutants to evaluate cholesterol transport function

  • N-terminal sorting signal mutants to alter subcellular localization

Context-Dependent Experimental Design:

• For ion channel modulation studies:

  • Electrophysiological recordings with wild-type vs. domain-specific mutants

  • Compare STOML1 effects across different channel subtypes

  • Assess in both heterologous expression systems and native neuronal contexts

• For cholesterol transport studies:

  • Fluorescent cholesterol tracking with domain-specific mutants

  • Lipidomic analysis of membrane compartments

  • Correlation between STOML1 levels and cholesterol distribution

Integrated Multi-Omics Approaches:

• Combine proteomics, lipidomics, and functional assays to build comprehensive models of STOML1 function

• Consider tissue-specific contexts, as STOML1 may have different functions in different cell types

• Use temporal dynamics to distinguish primary from secondary effects

These experimental strategies can help delineate STOML1's multiple functions and determine how they are coordinated through its unique domain structure in different cellular contexts.