Recombinant Rat Lysosomal-associated transmembrane protein 4A (Laptm4a)
Description
Protein Family Classification
Lysosomal-associated transmembrane protein 4A (Laptm4a) belongs to a family of conserved proteins found across diverse taxonomic groups including mammals, insects, and nematodes . This evolutionary conservation suggests fundamental biological roles essential to eukaryotic cellular function. The LAPTM family includes several homologous proteins that share structural similarities while potentially serving specialized functions in different tissues and cellular compartments. Among these family members, Laptm4a has garnered particular interest due to its involvement in molecular transport processes and potential implications in drug response mechanisms.
Evolutionary Conservation and Significance
The high degree of conservation observed in Laptm4a across multiple species indicates its essential biological functions that have been maintained throughout evolutionary history. This conservation extends to the rat version of the protein, which shares significant homology with human and other mammalian counterparts . The rattus norvegicus (rat) Laptm4a, identified by UniProt accession number Q6P501, represents an important model for understanding the protein's function in mammalian systems . Its study provides insights that may be translatable to human biology while offering specific advantages for experimental investigation in controlled laboratory settings.
Protein Architecture and Domains
Rat Laptm4a consists of 233 amino acids forming a complex transmembrane protein with distinctive structural features . The protein contains four putative membrane-spanning domains that anchor it within cellular membranes . A notable structural feature is its 55 amino acid C-terminal region that faces the cytoplasm, which plays a crucial role in the protein's localization and function . The full amino acid sequence of rat Laptm4a reveals a protein rich in hydrophobic regions consistent with its membrane-embedded nature, while also containing functional motifs essential for its biological activities and cellular interactions .
Key Motifs and Functional Elements
The cytoplasmic domain of Laptm4a contains two tandemly arranged tyrosine-containing motifs that are critical for its proper localization to endosomal and lysosomal compartments . These motifs function as sorting signals, directing the protein to its appropriate cellular destinations through interactions with vesicular trafficking machinery. Interestingly, Laptm4a represents a unique case among membrane proteins targeting endosomes/lysosomes, as it requires both tyrosine-based sorting signals working in tandem, rather than independent signals, for efficient compartmentalization . This distinctive requirement suggests specialized regulatory mechanisms controlling Laptm4a distribution and function within cells.
Endosomal and Lysosomal Targeting
Laptm4a predominantly localizes to endosomes and lysosomes within cells, with its distribution tightly regulated by specific sorting signals . Experimental evidence demonstrates that even under conditions of transient high-level expression in cultured cells, Laptm4a remains efficiently targeted to internal vesicular compartments with no detectable protein on the cell surface . This strict intracellular retention indicates sophisticated cellular mechanisms controlling Laptm4a distribution, reflecting its specialized functions within endosomal-lysosomal compartments.
Sorting Signal Requirements
The efficient localization of Laptm4a to vesicles containing lysosomal markers depends critically on its unique dual tyrosine-containing motifs in the cytoplasmic domain . Mutagenic analysis has confirmed that both motifs must function together for proper targeting, distinguishing Laptm4a from many other endosomal/lysosomal proteins that possess independently functioning sorting signals . This unique requirement suggests that Laptm4a trafficking may involve specialized adaptor proteins or regulatory mechanisms controlling its movement between cellular compartments, potentially allowing for finely tuned responses to cellular conditions.
Regulation of Molecular Transport
A primary function of Laptm4a involves regulating the intracellular compartmentalization of amphipathic solutes, suggesting an important role in molecular transport across cellular membranes . This function may influence the distribution and concentration of various compounds within cellular compartments, potentially affecting their bioavailability and activity. By controlling molecular transport between compartments, Laptm4a contributes to maintaining proper cellular homeostasis and compartmentalization of function.
Drug Sensitivity Modulation
Laptm4a has been implicated in modulating cellular sensitivity toward various compounds including anthracyclines, antibiotics, ionophores, nucleobases, and organic cations . This ability to influence drug responses bears similarities to the multidrug-resistance phenotype exhibited by cells expressing high levels of P-glycoprotein . The precise mechanisms underlying this function remain under investigation, but may involve changes in drug compartmentalization, efflux, or accessibility to cellular targets. This property highlights Laptm4a's potential significance in therapeutic contexts and drug development strategies.
Immunological Applications
Recombinant rat Laptm4a serves as a valuable tool for immunological studies, including the development and validation of antibodies targeting this protein . These antibodies enable detection and characterization of Laptm4a expression patterns in different tissues and cell types, contributing to our understanding of its distribution and regulation. Immunohistochemistry, immunofluorescence, and ELISA applications utilizing recombinant Laptm4a and corresponding antibodies provide crucial insights into the protein's expression and localization under various physiological and pathological conditions.
Functional Studies and Protein Interactions
The availability of purified recombinant rat Laptm4a facilitates detailed investigations of its functional properties and molecular interactions. Researchers can use the recombinant protein in binding studies to identify interaction partners, in vitro transport assays to characterize its transport functions, and structure-function analyses to determine the contributions of specific domains to its various activities. These applications advance our understanding of Laptm4a's biological roles and its integration within cellular pathways.
Comparative Studies Between Species
Recombinant rat Laptm4a enables comparative studies with homologous proteins from other species, including humans, providing insights into both conserved and species-specific aspects of its function . Such comparative approaches help identify essential functional elements maintained throughout evolution while also highlighting specialized adaptations that may have emerged in different organisms. These comparisons are valuable for translating findings from rat models to human applications, particularly in the context of disease mechanisms and therapeutic development.
Potential Role in Drug Resistance
The ability of Laptm4a to modulate cellular sensitivity to various compounds suggests its potential involvement in drug resistance mechanisms . Understanding how Laptm4a contributes to these processes could reveal new strategies for overcoming therapeutic resistance in various diseases, particularly cancer. The similarities between Laptm4a-mediated effects and P-glycoprotein-associated multidrug resistance indicate potentially overlapping or complementary mechanisms that warrant further investigation in clinical contexts.
Therapeutic Target Possibilities
Given its functions in molecular transport and drug sensitivity modulation, Laptm4a represents a potential target for developing novel chemotherapeutic strategies . Interventions that modify Laptm4a activity or expression could potentially enhance the efficacy of existing treatments by altering drug compartmentalization or cellular responses. The recombinant rat protein serves as a valuable tool for screening and developing such targeted interventions through in vitro assays and structural studies.
Expression Patterns in Normal and Pathological States
Research utilizing recombinant rat Laptm4a and related tools continues to elucidate the protein's expression patterns across different tissues and under various physiological and pathological conditions. Studies examining differential expression in models of disease, including hypertension, provide insights into potential roles of Laptm4a in specific pathologies . These investigations help identify contexts where Laptm4a function may be particularly relevant to disease mechanisms or therapeutic interventions.
Future Research Priorities
Several key areas warrant further investigation to advance our understanding of recombinant rat Laptm4a and its applications. These include more detailed structural characterization using advanced techniques like cryo-electron microscopy, comprehensive mapping of its interactome to identify functional partners, and expanded studies of its roles in specific disease models. Additionally, translational research comparing findings between rat models and human systems will be crucial for establishing the clinical relevance of Laptm4a-focused interventions.
Product Specs
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Note: All our proteins are shipped with standard blue ice packs. If you require dry ice shipping, please contact us in advance as additional fees will apply.
Generally, the shelf life of liquid form is 6 months at -20°C/-80°C. The shelf life of lyophilized form is 12 months at -20°C/-80°C.
Target Background
Q&A
What is the basic structure of LAPTM4A?
LAPTM4A belongs to a family of conserved proteins found in mammals, insects, and nematodes. The protein contains four putative membrane-spanning domains and a 55 amino acid C-terminal region that faces the cytoplasm . This structure is critical for its function in cellular compartmentalization. When designing experiments to study LAPTM4A structure-function relationships, researchers should consider both transmembrane domains and the cytoplasmic tail, as both elements contribute to protein localization and interaction capabilities.
What are the key sorting signals in LAPTM4A?
LAPTM4A contains two tandemly arranged tyrosine-containing motifs in its cytoplasmic domain that are required for efficient localization to vesicles containing lysosomal markers . These tyrosine-based sorting signals are unique because both are required simultaneously, unlike other lysosomal proteins that typically contain independently functioning sorting signals. When designing LAPTM4A mutants for localization studies, both tyrosine motifs should be considered as targets for mutagenesis to fully understand trafficking mechanisms.
Where is LAPTM4A primarily localized in cells?
LAPTM4A is primarily localized to endosomes and lysosomes . Its localization appears to be tightly controlled, as even transient high-level expression of LAPTM4A in cultured cells results in no detectable protein on the cell surface . In human kidney tissue, LAPTM4A shows partial colocalization with transporters like hOCT2 in submembraneous vesicular structures of proximal tubule cells, specifically in lysosomes and late endosomes . To properly study LAPTM4A localization, confocal microscopy with markers for lysosomes (LAMP1) and late endosomes is recommended.
How does LAPTM4A differ from LAPTM4B in terms of cellular localization?
While both LAPTM4A and LAPTM4B localize to lysosomes, LAPTM4B is unique in that a fraction of it is also present at the plasma membrane . Additionally, LAPTM4B overexpression induces the formation of actin-based membrane protrusions, which is not observed with LAPTM4A . When studying the LAPTM family, it's important to use specific antibodies or tags that can distinguish between these closely related proteins to avoid misattribution of observed effects.
What proteins interact with LAPTM4A and how can these interactions be studied?
LAPTM4A interacts with the E3 ubiquitin ligase Nedd4, similar to other LAPTM family members . This interaction depends on the PY motifs in LAPTM4A. Additionally, LAPTM4A has been identified as an interaction partner of the human organic cation transporter 2 (hOCT2) . To study these interactions, researchers have successfully employed:
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Mating-based split ubiquitin yeast two-hybrid system (mbSUS) - especially useful for membrane proteins as interactions take place at the plasma membrane
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HIS-pulldown assays for in vitro confirmation
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FRET analysis to detect interactions in living cells
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Co-immunoprecipitation experiments
These methodologies can be applied sequentially to establish and characterize novel LAPTM4A protein interactions with increasing levels of confidence.
How does the interaction between LAPTM4A and Nedd4 affect cellular processes?
The interaction between LAPTM4A and Nedd4 plays a significant role in membrane sorting. In Nedd4 knockout mouse embryonic fibroblasts (MEFs), LAPTM4A shows reduced lysosomal localization . This suggests that Nedd4 is critical for proper trafficking of LAPTM4A to lysosomes. When designing experiments to investigate this interaction, researchers should consider establishing Nedd4-deficient cell models through knockout or knockdown approaches to assess changes in LAPTM4A localization.
What is the role of LAPTM4A in cellular transport mechanisms?
LAPTM4A functions to regulate the intracellular compartmentalization of amphipathic solutes and possibly the sensitivity of cells toward anthracyclines, antibiotics, ionophores, nucleobases, and organic cations . This function is similar to the multidrug-resistance phenotype exhibited by cells synthesizing high levels of P-glycoprotein. In specific relation to transport, LAPTM4A has been shown to regulate the function of hOCT2 by influencing its trafficking to/from the cell membrane . When overexpressed, LAPTM4A leads to a significant reduction in hOCT2-mediated substrate uptake (by approximately 23%) .
How does LAPTM4A affect organic cation transport?
LAPTM4A regulates the function of human organic cation transporter 2 (hOCT2) through an interaction that occurs in lysosomes and late endosomes . This interaction appears to induce endocytotic degradation of hOCT2. In functional studies using the fluorescent organic cation ASP+ as a substrate for OCTs, overexpression of LAPTM4A led to a significant reduction in ASP+ uptake by 23 ± 3% in hOCT2-expressing cells . This suggests LAPTM4A plays a role in controlling the cell surface availability of transport proteins.
A typical experimental setup to study this interaction includes:
| Experimental Group | Description | Typical Result |
|---|---|---|
| Control cells | hOCT2 stably transfected cells | Baseline ASP+ uptake |
| Vehicle control | hOCT2 cells transiently transfected with empty vector | No significant change in ASP+ uptake |
| LAPTM4A overexpression | hOCT2 cells transiently transfected with LAPTM4A | 23% reduction in ASP+ uptake |
How is LAPTM4A expressed in different tissues and cell types?
LAPTM4A shows significant expression in human kidney, particularly in proximal tubule cells . It is also expressed in HEK293 cells, which makes them a suitable model for studying LAPTM4A function. In kidney tissue, LAPTM4A is expressed in all tubular segments . For detection of endogenous LAPTM4A expression, researchers have successfully used:
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RT-PCR with LAPTM4A-specific primers to detect mRNA expression
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Western blot analysis with anti-LAPTM4A antibodies for protein detection
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Immunofluorescence microscopy for localization studies
What methodologies can be used to study LAPTM4A trafficking?
To study LAPTM4A trafficking and localization, researchers can employ:
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Fluorescent protein tagging (e.g., mCherry-LAPTM4A constructs)
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Colocalization studies with organelle markers (e.g., LAMP1 for lysosomes)
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Cell surface biotinylation assays to detect potential surface expression
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Mutagenesis of sorting signals followed by localization analysis
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Live-cell imaging to track protein movement in real-time
When conducting colocalization studies, quantification using the Pearson's correlation coefficient provides a statistical measure of colocalization with specific organelle markers .
How can recombinant rat LAPTM4A be effectively overexpressed in experimental systems?
For overexpression of rat LAPTM4A in experimental systems, adenoviral vectors provide an efficient delivery method. Adenovirus expressing rat LAPTM4A under the CMV promoter is commercially available . For optimal results when working with adenoviral vectors:
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Aliquot vectors into low protein binding tubes upon receipt to avoid repeated freeze-thaw cycles
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Validate expression using appropriate detection methods (Western blot, immunofluorescence)
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Optimize transduction conditions (MOI, incubation time) for your specific cell type
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Include appropriate controls (empty vector, GFP-expressing vector)
What are the considerations when designing LAPTM4A mutants for functional studies?
When designing LAPTM4A mutants for functional studies, researchers should consider:
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The critical role of tyrosine-containing motifs in the cytoplasmic domain for lysosomal localization
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The importance of PY motifs for interaction with Nedd4 and proper sorting
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The four transmembrane domains that may contribute to protein stability and folding
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Appropriate tagging strategies that don't interfere with protein function
Mutation of the tandemly arranged tyrosine-containing motifs can significantly affect localization patterns and should be carefully controlled and quantified using markers like lysosomal glycoprotein 120 .
Why might LAPTM4A be considered a potential therapeutic target?
LAPTM4A's function in regulating the intracellular compartmentalization of amphipathic solutes and its potential influence on cell sensitivity toward various compounds (anthracyclines, antibiotics, ionophores, nucleobases, and organic cations) resembles the multidrug-resistance phenotype associated with P-glycoprotein . This functional similarity suggests LAPTM4A could potentially be a suitable target for developing novel chemotherapeutic agents. Additionally, its role in regulating transporters like hOCT2 may have implications for drug delivery and efficacy in organs like the kidney.
What experimental approaches would be suitable for exploring LAPTM4A as a therapeutic target?
To investigate LAPTM4A as a potential therapeutic target, researchers could employ:
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Small molecule screening to identify compounds that modulate LAPTM4A function
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CRISPR/Cas9-mediated knockout or knockdown studies to determine the effects of LAPTM4A deficiency on drug sensitivity
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Structure-based drug design targeting the interaction interfaces with Nedd4 or transporters
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In vivo models with altered LAPTM4A expression to evaluate physiological impacts
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Combination studies with existing therapeutics to identify potential synergistic effects
How does LAPTM4A compare functionally to other LAPTM family members?
LAPTM4A belongs to a family that includes LAPTM4B and LAPTM5. While all three localize to lysosomes, there are significant functional differences:
Understanding these differences is crucial when designing experiments to study specific family members and interpreting results in the context of cellular physiology.
