Biochemical and topological properties of type A MGDG synthase, a spinach chloroplast envelope enzyme catalyzing the synthesis of both prokaryotic and eukaryotic MGDG

Eur J Biochem. 1999 Nov;265(3):990-1001. doi: 10.1046/j.1432-1327.1999.00801.x.


MGDG synthase, the enzyme that catalyzes the synthesis of the major chloroplast membrane lipid monogalactosyldiacylglycerol (MGDG), is encoded by a multigenic family. We have analyzed the biochemical properties, subcellular localization and membrane topology of a spinach chloroplast MGDG synthase, a representative member of the type A family from Spinacia oleracea (soMGD A), using a recombinant protein that was functionally overexpressed in Escherichia coli and specific polyclonal antibodies. We demonstrated that soMGD A could catalyze the synthesis of both 'prokaryotic' and 'eukaryotic' MGDG molecular species in vitro, with a selectivity for diacylglycerol similar to that of purified chloroplast envelope MGDG synthase activity. Furthermore, soMGD A was shown to be sensitive to chemical reagents (dithiothreitol, N-ethylmaleimide and o-phenanthroline) known to affect MGDG synthesis by the partially purified enzyme, as well as in isolated chloroplast envelope membranes. In spinach chloroplasts, soMGD A was localized by Western blot analysis in the inner envelope membrane. Topological studies demonstrated that soMGD A is a monotopic enzyme, embedded within one leaflet of the inner envelope membrane from spinach chloroplasts, a structure which may involve amphipathic alpha helices. We further demonstrated that in vitro, soMGD A precursor is imported and processed to its correct mature form in intact chloroplasts. These results show that soMGD A corresponds to a mature polypeptide of approximately 45 kDa. In addition, inactivation kinetics after gamma-ray irradiation strongly suggest that both native chloroplast envelope MGDG synthase and recombinant soMGD A have a functional molecular mass of 95-100 kDa, indicating that they are probably active as homodimers made of two 45-kDa subunits. This study suggests that, in spite of the growing evidence that MGDG synthesis is catalyzed by a multigenic family of enzymes, in spinach leaves both prokaryotic and eukaryotic MGDG syntheses could be attributable to a unique dimeric enzyme, provided that diacylglycerol is transported from the outer membrane to the inner membrane of the chloroplast envelope.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Chloroplasts / enzymology
  • Cloning, Molecular
  • DNA Primers / genetics
  • DNA, Complementary / genetics
  • DNA, Plant / genetics
  • Diglycerides / biosynthesis*
  • Dimerization
  • Escherichia coli / genetics
  • Galactolipids*
  • Galactosyltransferases / chemistry*
  • Galactosyltransferases / genetics
  • Galactosyltransferases / metabolism*
  • Glycolipids / biosynthesis*
  • Intracellular Membranes / enzymology
  • Kinetics
  • Molecular Sequence Data
  • Molecular Weight
  • Protein Structure, Quaternary
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Spinacia oleracea / enzymology*
  • Spinacia oleracea / genetics


  • DNA Primers
  • DNA, Complementary
  • DNA, Plant
  • Diglycerides
  • Galactolipids
  • Glycolipids
  • Recombinant Proteins
  • monogalactosyldiacylglycerol
  • Galactosyltransferases
  • 1,2-diacylglycerol 3-beta-galactosyltransferase

Associated data

  • GENBANK/AJ249607