Recombinant Human Tail-anchored protein insertion receptor WRB (WRB)
Description
Introduction to Recombinant Human WRB and Its Role in Tail-Anchored Protein Insertion
WRB (Wnt1 Responsive Bone protein), also known as CHD5 (Congenital Heart Disease Protein 5), is a transmembrane receptor critical for the post-translational insertion of tail-anchored (TA) proteins into the endoplasmic reticulum (ER) membrane. Recombinant WRB refers to engineered versions of this protein produced in vitro for experimental or therapeutic purposes. It functions as part of the TRC40 pathway, collaborating with CAML (Calcium-Modulating Cyclophilin Ligand) to mediate TA protein targeting and membrane integration .
Functional Interactions of WRB with TRC40 and CAML
WRB forms a heterodimeric receptor complex with CAML, which is essential for TRC40-mediated TA protein insertion. Below are key findings from biochemical and structural studies:
Mechanistic Insights:
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WRB recruits TRC40 to the ER membrane, enabling TA protein delivery .
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CAML stabilizes WRB, and its absence destabilizes WRB mRNA, leading to reduced protein levels .
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WRB’s coiled-coil domain competitively inhibits TRC40-mediated insertion in vitro, confirming its role as a docking site .
Experimental Applications of Recombinant WRB Domains
Recombinant WRB variants have been instrumental in elucidating its function:
3.1. Soluble Coiled-Coil Domain (WRBcc)
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Expression: Purified WRBcc (fused to maltose-binding protein) was expressed in E. coli and used to study TRC40 binding .
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Function: WRBcc directly binds TRC40 and blocks TA protein insertion in vitro, reducing glycosylation of substrates like HZZ-RAMP4op by up to 92% .
| TA Protein | Inhibition by WRBcc | Experimental System | Source |
|---|---|---|---|
| HZZ-RAMP4op | 92% reduction | Rough microsomes (RMs) | |
| Cytochrome b5 (Cb5) | Partial reduction | TRC40-dependent insertion |
3.2. In Vitro Membrane Reconstitution
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Proteoliposomes: Recombinant WRB and CAML were reconstituted into liposomes to mimic ER membrane targeting. These liposomes supported TRC40-dependent TA protein insertion, confirming the sufficiency of WRB-CAML for this process .
In Vivo Studies: Tissue-Specific Roles of WRB
Mouse models with tissue-specific WRB knockouts revealed critical dependencies:
Key Findings:
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Syntaxin 5 (Stx5) exhibited extreme sensitivity to WRB depletion, linked to its aggregation-prone cytoplasmic domain .
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CAML stability depends on WRB; WRB knockout leads to CAML degradation via the proteasome .
5.1. Implications for Disease
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Congenital Heart Disease: WRB is located on chromosome 21 and implicated in Down syndrome-associated heart defects .
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Hearing Loss: WRB-deficient hair cells show reduced otoferlin levels, critical for mechanotransduction .
5.2. Technical Limitations
Product Specs
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Target Background
- The WRB gene contains a maternally imprinted differentially methylated region (DMR). Maternally inherited 5mCpG imprints at the WRB DMR are not coupled to the parental allele expression of WRB and ten neighboring genes across twelve tissue types (brain, blood, fallopian tube, fetal large and small intestine, hESCs, large airway epithelial cells, thyroid, muscle, epidermal keratinocytes, ovary, skin, and testis). PMID: 27100087
- Studies identify calcium-modulating cyclophilin ligand (CAML) and WRB as components of the TRC40 receptor complex, a critical mechanism for ER membrane insertion of TA proteins in mammalian cells. PMID: 23041287
- The coiled-coil domain of WRB serves as the binding site for TRC40/Asna1. PMID: 21444755
