The delivery of copper for thylakoid import observed by NMR

Proc Natl Acad Sci U S A. 2006 May 30;103(22):8320-5. doi: 10.1073/pnas.0600142103. Epub 2006 May 17.

Abstract

The thylakoid compartments of plant chloroplasts are a vital destination for copper. Copper is needed to form holo-plastocyanin, which must shuttle electrons between photosystems to convert light into biologically useful chemical energy. Copper can bind tightly to proteins, so it has been hypothesized that copper partitions onto ligand-exchange pathways to reach intracellular locations without inflicting damage en route. The copper metallochaperone Atx1 of chloroplast-related cyanobacteria (ScAtx1) engages in bacterial two-hybrid interactions with N-terminal domains of copper-transporting ATPases CtaA (cell import) and PacS (thylakoid import). Here we visualize copper delivery. The N-terminal domain PacS(N) has a ferredoxin-like fold that forms copper-dependent heterodimers with ScAtx1. Removal of copper, by the addition of the cuprous-ion chelator bathocuproine disulfonate, disrupts this heterodimer, as shown from a reduction of the overall tumbling rate of the protein mixture. The NMR spectral changes of the heterodimer versus the separate proteins reveal that loops 1, 3, and 5 (the carboxyl tail) of the ScAtx1 Cu(I) site switch to an apo-like configuration in the heterodimer. NMR data ((2)J(NH) couplings in the imidazole ring of (15)N ScAtx1 His-61) also show that His-61, bound to copper(I) in [Cu(I)ScAtx1](2), is not coordinated to copper in the heterodimer. A model for the PacS(N)/Cu(I)/ScAtx1 complex is presented. Contact with PacS(N) induces change to the ScAtx1 copper-coordination sphere that drives copper release for thylakoid import. These data also elaborate on the mechanism to keep copper(I) out of the ZiaA(N) ATPase zinc sites.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Transport
  • Copper / chemistry*
  • Copper / metabolism*
  • Dimerization
  • Ligands
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Molecular Conformation
  • Thylakoids / chemistry*
  • Thylakoids / metabolism*

Substances

  • Ligands
  • Copper

Associated data

  • PDB/2GCF