Protein Engineering, Vol. 13, No. 11, 811-817,
November 2000
© 2000 Oxford University Press
Functional expression in insect cells, one-step purification and characterization of a recombinant phospholipase D from cowpea (Vigna unguiculata L. Walp)
UPR 9025 du CNRS, Laboratoire de Lipolyse Enzymatique,31 Chemin Joseph-Aiguier, 13402 Marseille Cedex 20, France
Phospholipase D (PLD) is an important enzyme involved in signal transduction, vesicle trafficking and membrane metabolism. In this study, large amounts of a recombinant plant PLD
were secreted into the culture medium of baculovirus-infected insect cells and purified to homogeneity in the form of a fully active enzyme. The transient production of recombinant PLD
yielded a protein (rPLD
a, 88 kDa) together with a shorter form (rPLD
b, 87 kDa), which accumulated in the medium. N-Terminal amino acid sequencing of the rPLD
a and rPLD
b showed that rPLD
b resulted from proteolytic cleavage at Gly8Ile9. Immunoblotting showed that both rPLD
a and rPLD
b are recognized by a polyclonal antibody previously raised against native soybean PLD
. One-step calcium-dependent octyl-Sepharose chromatography was used to obtain the two highly purified forms of rPLD
, as attested by gel electrophoresis, N-terminal amino acid sequence and mass spectrometry. The N-terminal region of PLD
is homologous with the C2 domains which are present in a number of enzymes known to be involved in signal transduction and/or phospholipid metabolism. The truncated rPLD
b lacks the first acidic amino acid in its N-terminus, which is probably involved in the calcium binding site. The rPLD
b was thus easily eluted from the octyl-Sepharose column by decreasing the calcium concentration of the buffer from 50 to 30 mM, whereas, the rPLD
a was eluted after chelating calcium ions with EDTA. The purified rPLD
yield reached a level of 10 mg per liter of serum-free culture medium. The availability of baculovirus-derived rPLD
constitutes a valuable source of enzyme for future crystallographic studies to determine its three-dimensional structure.