Casparian strip membrane protein 5 (PtCASP5) is a small tetraspan plasma-membrane protein of the CASP (Casparian Strip membrane domain Protein) family, built around a central MARVEL-like four-transmembrane domain. CASP proteins are not enzymes; they self-organize into a stable, immobile membrane scaffold at the Casparian strip membrane domain of the root endodermis, recruiting the lignin-polymerization machinery that drives localized lignin deposition in the adjacent cell wall. The resulting Casparian strip forms an apoplastic diffusion barrier governing selective uptake of water and solutes. The protein localizes to the plasma membrane in a restricted belt-shaped band and forms homodimers and heterodimers with other CASP family members.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: CASP5 is a multi-pass plasma-membrane protein of the CASP family; plasma membrane localization is the well-supported core cellular component. Reason: UniProt reports cell membrane (plasma membrane) localization as a multi-pass membrane protein, consistent with the CASP family and the four predicted transmembrane helices in the sequence record. Supporting Evidence: file:POPTR/CASP5/CASP5-uniprot.txt SUBCELLULAR LOCATION: Cell membrane file:POPTR/CASP5/CASP5-uniprot.txt DR GO; GO:0005886; C:plasma membrane; IBA:GO_Central. |
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Download this section (compressed HTML)Q: Is PtCASP5 expressed specifically in the root endodermis and localized to the Casparian strip membrane domain in poplar, as predicted from its Arabidopsis orthologs?
Experiment: Express a fluorescently tagged PtCASP5 in poplar roots and image its subcellular localization to test for a belt-shaped Casparian strip membrane domain band in the endodermis.
Type: localization imaging
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