Recombinant Human Vesicle-associated membrane protein 5 (VAMP5)

What is VAMP5 and what is its structural profile?

VAMP5 (vesicle-associated membrane protein 5) is a member of the synaptobrevin family of proteins. It is a type IV transmembrane protein (a type II TM protein whose C-terminus is almost completely transmembrane) found in both trans-Golgi and plasma membranes of myotubes (mature skeletal and cardiac muscle cells). Human VAMP5 is 116 amino acids in length and contains an N-terminal cytoplasmic region (amino acids 1-72) with one vSNARE coiled-coil homology domain, a 21-amino acid transmembrane segment, and a 23-amino acid C-terminal luminal domain . The protein has a predicted molecular weight of 11 kDa but runs anomalously at 16 kDa in SDS-PAGE, suggesting post-translational modifications that affect its electrophoretic mobility .

How does VAMP5 differ from other VAMP family members?

Unlike other VAMPs that are commonly associated with vesicle fusion to t-SNAREs in cell membranes, VAMP5 appears to show no such activity . VAMP5 is specifically expressed by Müller cells in the retina and is contained in a subset of their extracellular vesicles (EVs) . This contrasts with VAMP8, which is involved in autophagy by directly regulating autophagosome membrane fusion and has been implicated in tumor progression . VAMP5's expression pattern is also more restricted compared to more broadly expressed VAMP family members. Over amino acids 1-72, human VAMP5 shares 75% amino acid identity with mouse VAMP5, indicating a relatively high degree of evolutionary conservation .

What tissues and cell types express VAMP5?

VAMP5 shows a distinct expression pattern with primary localization in:

• Skeletal muscle cells, specifically in the sarcoplasm of muscle cells as demonstrated by immunohistochemical staining

• Cardiac muscle cells (myotubes)

• Müller cells, a type of radial glial cells in the retina that form part of the central nervous system

In retinal Müller cells, VAMP5 is expressed in specialized domains including endfeet facing the vitreous body and microvilli surrounding photoreceptor segments .

What is the subcellular localization of VAMP5?

VAMP5 is primarily localized to:

• Trans-Golgi membranes

• Plasma membranes of myotubes

• Extracellular vesicles released from specialized domains of Müller cells

This subcellular distribution suggests VAMP5 plays a role in membrane trafficking between the Golgi apparatus and the cell surface, particularly in specialized cell types like muscle cells and retinal Müller cells.

What is the role of VAMP5 in extracellular vesicle formation and release?

Recent research has demonstrated that VAMP5 is a component of extracellular vesicles (EVs) released by Müller cells in the retina . These cells release distinct EVs from their endfeet facing the vitreous body and from their microvilli surrounding photoreceptor segments . VAMP5-positive EVs bear a characteristic protein composition that differs substantially from those secreted by neurons . This suggests that VAMP5 may play a specific role in the biogenesis, cargo selection, or targeting of these specialized EVs.

Methodologically, researchers investigating VAMP5's role in EV formation should:

• Utilize immunoaffinity purification of cell-specific EVs using VAMP5 antibodies

• Perform comparative proteomics between VAMP5-positive and VAMP5-negative EVs

• Employ electron microscopy to visualize the subcellular localization of VAMP5 in EV-releasing domains

• Use RNA-seq analysis to identify transcriptional changes associated with VAMP5 expression in EV-producing cells

How does VAMP5 respond to ischemic conditions?

VAMP5 has been identified as responsive to ischemia in Müller cells of the retina . Under ischemic conditions, the expression pattern and possibly the function of VAMP5 changes, suggesting it may play a role in cellular adaptation to reduced oxygen availability. This responsiveness could indicate a neuroprotective function for VAMP5-containing EVs in the context of retinal ischemia.

To study this phenomenon, researchers should consider:

• Establishing in vitro oxygen-glucose deprivation models using Müller cell cultures

• Quantifying VAMP5 expression and localization changes using immunofluorescence and subcellular fractionation

• Analyzing the cargo composition of VAMP5-positive EVs under normal versus ischemic conditions

• Employing in vivo retinal ischemia models to validate in vitro findings

What techniques are most effective for studying VAMP5 interactions with other SNARE proteins?

As a SNARE component, VAMP5 may interact with other SNARE proteins, although its activity appears different from typical VAMP proteins . To study these interactions:

• Co-immunoprecipitation with specific antibodies against VAMP5 and potential SNARE partners

• Proximity ligation assays to detect in situ protein-protein interactions

• FRET (Förster Resonance Energy Transfer) analysis using fluorescently-tagged VAMP5 and other SNAREs

• In vitro reconstitution assays to test SNARE complex formation

• Hydrogen-deuterium exchange mass spectrometry to map interaction interfaces

These approaches provide complementary data on both the occurrence and the molecular details of potential SNARE interactions involving VAMP5.

What is the relationship between VAMP5 expression and cellular differentiation?

Given VAMP5's specific expression in mature muscle cells (myotubes) and specialized glial cells (Müller cells), it likely plays a role in terminal differentiation or specialized functions of these cell types. Researchers investigating this relationship should:

• Track VAMP5 expression during myoblast-to-myotube differentiation using qPCR and Western blotting

• Perform knockdown/knockout experiments to determine if VAMP5 is necessary for proper differentiation

• Analyze transcriptomic changes associated with VAMP5 expression during differentiation

• Investigate whether VAMP5-positive EVs contribute to paracrine signaling during differentiation

What expression systems are optimal for producing recombinant human VAMP5?

Based on the available data and protein characteristics, researchers should consider:

• E. coli expression system: Effective for producing the cytoplasmic domain (amino acids 2-72) of human VAMP5, as demonstrated by the successful production of recombinant human VAMP5 for antibody generation

• Mammalian expression systems: For full-length VAMP5 with proper membrane insertion and post-translational modifications, consider:

  • HEK293 cells for high yield

  • Muscle cell lines (C2C12, differentiated to myotubes) for native-like processing

• Optimization parameters:

What are the optimal antibodies and detection methods for studying VAMP5?

For effective detection of VAMP5 in research applications:

• Validated antibodies: Affinity-purified polyclonal antibodies against human VAMP5, such as Sheep Anti-Human VAMP5 Antigen Affinity-purified Polyclonal Antibody, have been successfully used for immunohistochemical detection in human skeletal muscle tissue

• Detection protocols:

  • Immunohistochemistry: 15 μg/mL antibody concentration, overnight incubation at 4°C

  • Western blotting: Account for anomalous migration (16 kDa versus predicted 11 kDa)

  • Immunofluorescence: Co-staining with cellular compartment markers to identify precise subcellular localization

• Controls:

  • Positive control: Human skeletal muscle tissue sections

  • Negative control: Tissues known not to express VAMP5

  • Specificity validation: Pre-adsorption with recombinant VAMP5 protein

How should researchers design experiments to study VAMP5's role in EVs?

To effectively investigate VAMP5's function in extracellular vesicle biology:

• EV isolation protocols:

  • Differential ultracentrifugation (standard approach)

  • Size exclusion chromatography (for improved purity)

  • Immunoaffinity capture using VAMP5 antibodies (for VAMP5-specific EVs)

• Characterization methods:

  • Nanoparticle tracking analysis for size distribution and concentration

  • Electron microscopy for morphological analysis

  • Western blotting for VAMP5 and common EV markers

  • Proteomics analysis for comprehensive cargo profiling

• Functional assays:

  • Uptake experiments using labeled EVs to track recipient cell targeting

  • Functional transfer assays to determine biological effects of VAMP5-positive EVs

  • VAMP5 knockdown/overexpression to assess impact on EV production and composition

How should researchers analyze RNA-seq data related to VAMP5 expression?

When analyzing transcriptomic data involving VAMP5:

• Alignment and quantification:

  • Align trimmed reads to the reference genome (e.g., GRCm38 for mouse studies) using HISAT2

  • Estimate transcript abundance with the stringtie routine and express as fragments per kilobase pairs of transcripts per million reads (fpkm)

• Differential expression analysis:

  • Compare VAMP5 expression between different cell types (e.g., Müller cells versus neurons)

  • Analyze VAMP5 expression changes under different conditions (e.g., normal versus ischemic)

  • Identify co-expressed genes that may function in the same pathways

• Pathway analysis:

  • Determine cellular processes enriched in datasets with high VAMP5 expression

  • Compare VAMP5-associated pathways with those of other VAMP family members

How can researchers distinguish between VAMP5-specific functions and general SNARE activities?

This represents a significant challenge in VAMP5 research. Recommended approaches include:

• Domain swapping experiments: Replace specific domains of VAMP5 with corresponding domains from other VAMPs to identify regions responsible for VAMP5-specific functions

• Genetic approaches:

  • VAMP5-specific knockout/knockdown with rescue experiments

  • Compare phenotypes with knockdown of other VAMP family members

• Interaction studies:

  • Identify VAMP5-specific binding partners not shared with other VAMPs

  • Characterize SNARE complex formation (or lack thereof) compared to other VAMPs

• Cell type specificity:

  • Leverage VAMP5's restricted expression pattern to identify cell type-specific functions

  • Compare functions in cells that naturally express VAMP5 versus forced expression in other cell types

What is the potential role of VAMP5 in retinal pathologies?

Given VAMP5's expression in Müller cells and its responsiveness to ischemia , researchers should investigate:

• VAMP5 expression in retinal disease models:

  • Diabetic retinopathy

  • Age-related macular degeneration

  • Retinitis pigmentosa

  • Glaucoma

• Therapeutic potential:

  • Could VAMP5-positive EVs serve as biomarkers for retinal pathologies?

  • Do these EVs carry neuroprotective factors that could be harnessed therapeutically?

  • Could modulation of VAMP5 expression affect disease progression?

• Methodological approaches:

  • Animal models of retinal diseases combined with VAMP5 manipulation

  • Analysis of human vitreous samples for VAMP5-positive EVs in patients with retinal pathologies

  • Single-cell RNA-seq of retinal tissue to track cell-specific VAMP5 expression changes

How does VAMP5 differ functionally between muscle and neural tissues?

VAMP5 shows specific expression in both myotubes and retinal Müller cells, raising questions about tissue-specific functions:

• Comparative studies:

  • Proteomic analysis of VAMP5-containing complexes in different tissues

  • Subcellular localization patterns in muscle versus Müller cells

  • Different binding partners and regulatory mechanisms

• Developmental timing:

  • Expression patterns during muscle development versus retinal development

  • Potential roles in terminal differentiation in both tissues

• Experimental approach:

  • Tissue-specific conditional knockout models

  • In vitro differentiation models for both cell types with VAMP5 manipulation