A constituent of the chloroplast import complex represents a new type of GTP-binding protein

Plant J. 1995 Mar;7(3):401-11. doi: 10.1046/j.1365-313x.1995.7030401.x.

Abstract

The 34 kDa polypeptide of the outer envelope membranes from pea chloroplasts (OEP 34) is a major constituent of this membrane. OEP 34 is detected on polyacrylamide gels under non-reducing condition in association with OEP 75, the putative protein translocation pore. An antiserum against OEP 34 is able to co-immunoprecipitate the precursor of Rubisco small subunit from a partially purified import complex of chloroplast outer envelope membranes. A full-length cDNA clone coding for pea OEP 34 has been isolated. Analysis of the deduced amino acid sequence revealed typical and conserved sequence motifs found in GTP-binding proteins, making it a new and unique member of this superfamily. OEP 34 behaves as an integral constituent of the outer chloroplast envelope, which is anchored by its C-terminus into the membrane, while the majority of the protein projects into the cytoplasm. OEP 34 does not possess a cleavable N-terminal transit sequence but it is targeted to the chloroplasts and integrated into the outer membranes by internal sequence information which seems to be present in the C-terminal membrane anchor region. Productive integration of OEP 34 into the outer envelope requires, in contrast to other OEPs, protease-sensitive chloroplast surface components and is stimulated by ATP. The GTP binding specificity of OEP 34 is demonstrated by photo-affinity labelling in the presence of [alpha-32P]GTP. Overexpressed and purified OEP 34 possesses endogenous GTPase activity. These results indicate a possible regulatory function of OEP 34 in protein translocation into chloroplasts.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Biological Transport, Active
  • Chloroplasts / metabolism
  • Cloning, Molecular
  • DNA, Complementary / genetics
  • DNA, Plant / genetics
  • GTP-Binding Proteins / chemistry
  • GTP-Binding Proteins / genetics*
  • GTP-Binding Proteins / metabolism
  • Models, Biological
  • Molecular Sequence Data
  • Peas / genetics
  • Peas / metabolism
  • Plant Proteins / chemistry
  • Plant Proteins / genetics*
  • Plant Proteins / metabolism

Substances

  • DNA, Complementary
  • DNA, Plant
  • Plant Proteins
  • outer envelope membrane protein 34-kDa
  • GTP-Binding Proteins

Associated data

  • GENBANK/Z28341