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Proc Natl Acad Sci U S A. 2014 Dec 16;111(50):E5480-7. doi: 10.1073/pnas.1421545111. Epub 2014 Dec 2.

Evolution of a plant-specific copper chaperone family for chloroplast copper homeostasis.

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Department of Chemistry and Biochemistry, and.
Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, MA 01609.
Department of Chemistry and Biochemistry, and Institute of Genomics and Proteomics, University of California, Los Angeles, CA 90095; and


Metallochaperones traffic copper (Cu(+)) from its point of entry at the plasma membrane to its destination. In plants, one destination is the chloroplast, which houses plastocyanin, a Cu-dependent electron transfer protein involved in photosynthesis. We present a previously unidentified Cu(+) chaperone that evolved early in the plant lineage by an alternative-splicing event of the pre-mRNA encoding the chloroplast P-type ATPase in Arabidopsis 1 (PAA1). In several land plants, recent duplication events created a separate chaperone-encoding gene coincident with loss of alternative splicing. The plant-specific Cu(+) chaperone delivers Cu(+) with specificity for PAA1, which is flipped in the envelope relative to prototypical bacterial ATPases, compatible with a role in Cu(+) import into the stroma and consistent with the canonical catalytic mechanism of these enzymes. The ubiquity of the chaperone suggests conservation of this Cu(+)-delivery mechanism and provides a unique snapshot into the evolution of a Cu(+) distribution pathway. We also provide evidence for an interaction between PAA2, the Cu(+)-ATPase in thylakoids, and the Cu(+)-chaperone for Cu/Zn superoxide dismutase (CCS), uncovering a Cu(+) network that has evolved to fine-tune Cu(+) distribution.


Arabidopsis thaliana; Atx1; Cu-transfer; inner envelope; metal transporter

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