Recombinant Arabidopsis thaliana Copper transporter 6 (COPT6)

Molecular Structure and Key Features

COPT6 belongs to the conserved CTR/COPT family of high-affinity copper transporters. Its structural features include:

• Full-length sequence: 145 amino acids (1–145aa) with a molecular weight of ~17 kDa .

• Transmembrane domains: Contains two transmembrane helices (TM1 and TM2), critical for forming a pore-like structure in the plasma membrane .

• Methionine-rich motifs: Conserved Met residues (e.g., Met106 in TM2) are essential for copper transport efficiency, while Met27 in the N-terminal domain is dispensable under copper-replete conditions .

• His-tag modification: Recombinant COPT6 is typically fused with an N-terminal His tag (e.g., 6xHis) for affinity purification via nickel- or cobalt-based chromatography .

Functional Role of Native COPT6

While the recombinant protein serves as a research tool, its native counterpart plays critical roles in copper homeostasis:

• Copper uptake and distribution: Localized to the plasma membrane, COPT6 mediates copper influx and redistribution, particularly under copper-deficient conditions .

• Tissue-specific expression: Predominantly expressed in vascular tissues, reproductive organs (e.g., sepals, petals, pollen), and embryos .

• Regulation by SPL7: Expression is modulated by the transcription factor SPL7, which responds to copper availability .

• Interaction with homologs: Forms hetero-oligomers with COPT1 (root-specific transporter) and COPT5 (tonoplast-localized mobilizer) .

Key Mutant Phenotypes

Recombinant COPT6 Production and Applications

Recombinant COPT6 is produced via heterologous expression systems for functional studies:

• Expression hosts:

  • E. coli: Used for large-scale production, yielding soluble protein suitable for biochemical assays .

  • S. cerevisiae: Used to study copper transport activity in vivo, as COPT6 rescues yeast ctr1Δ ctr3Δ mutants .

• Purification: Affinity chromatography (His-tag), followed by size-exclusion chromatography for higher purity .

Common Applications

Research Findings and Significance

• Copper homeostasis: COPT6 facilitates shoot copper redistribution during deficiency, as shown by altered Cu distribution in copt6 mutants .

• Structural insights: The N-terminal domain enhances transport efficiency under low copper but is dispensable under copper-replete conditions .

• Cross-talk with iron: Overexpression of COPT6 or COPT2 disrupts iron homeostasis, suggesting regulatory interactions between copper and iron pathways .

Challenges and Future Directions

• Stability issues: Repeated freeze-thaw cycles reduce activity; storage at -20°C/-80°C is recommended .

• Functional redundancy: COPT6’s role overlaps with COPT1 and COPT2, requiring precise genetic or biochemical dissection .

• Biotechnological potential: Engineering COPT6 for enhanced copper uptake could improve crop resilience to copper-deficient soils .