OEP37 is a new member of the chloroplast outer membrane ion channels

J Biol Chem. 2006 Jun 30;281(26):17989-98. doi: 10.1074/jbc.M600700200. Epub 2006 Apr 19.

Abstract

The chloroplast outer envelope protein OEP37 is a member of the growing beta-barrel protein family of the outer chloroplast membrane. The reconstituted recombinant protein OEP37 from pea forms a rectifying high conductance channel with a main conductance (lambda) of Lambda= 500 picosiemens (symmetrical 250 mm KCl). The OEP37 channel is cation-selective (P(K+)/P(K-) = 14:1) with a voltage-dependent open probability maximal at V(mem) = 0 mV. The channel pore reveals an hourglass-shaped form with different diameters for the vestibule and restriction zone. The diameters of the vestibule at the high conductance side were estimated by d = 3.0 nm and the restriction zone by d = 1.5 nm. The OEP37 channel displayed a nanomolar affinity for the precursor of the chloroplast inner membrane protein Tic32, which is imported into the chloroplast through a yet unknown pathway. Pre-proteins imported through the usual Toc pathway and synthetic control peptides, however, did not show a comparable block of the OEP37 channel. In addition to the electrophysiological characterization, we studied the gene expression of OEP37 in the model plant Arabidopsis thaliana. Here, transcripts of AtOEP37 are ubiquitously expressed throughout plant development and accumulate in early germinating seedlings as well as in late embryogenesis. The plastid intrinsic protein could be detected in isolated chloroplasts of cotyledons and rosette leaves. However, the knock-out mutant oep37-1 shows that the proper function of this single copy gene is not essential for development of the mature plant. Moreover, import of Tic32 into chloroplasts of oep37-1 was not impaired when compared with wild type. Thus, OEP37 may constitute a novel peptide-sensitive ion channel in the outer envelope of plastids with function during embryogenesis and germination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / physiology*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / physiology*
  • Cations / metabolism
  • Chloroplasts / physiology*
  • Copper / pharmacology
  • Cotyledon / physiology
  • Gene Expression Regulation, Developmental
  • Gene Expression Regulation, Plant
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Ion Channels / genetics
  • Ion Channels / physiology*
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Mutagenesis
  • Peptides / pharmacology
  • Phenotype
  • Plant Leaves / physiology
  • Plastids / physiology
  • Potassium Chloride / pharmacology
  • Seedlings / physiology

Substances

  • Arabidopsis Proteins
  • Cations
  • Ion Channels
  • Peptides
  • Potassium Chloride
  • Copper