Cryoprotective members of the
WAX9 protein gene family lacking lipid transfer activity
Schilling, S.1, Sror, H.A.M.1,2, Köhn, C.1, Hincha, D.K.3,
and Schmitt, J.M. 1
1Institut für Biologie, Freie Universität, Königin Luise
Str. 12-16, 14195 Berlin, Germany
2 Biochemistry Department, Faculty of Agriculture,
Ain-shams University, Cairo, Egypt
3Max-Planck-Institut für Molekulare Pflanzenphysiologie,
14424 Potsdam, Germany
Nonspecific lipid transfer proteins (LTPs) are usually
organized as gene families in plants. The molecules are
characterized by four conserved disulfide bonds. Their
physiological function in vivo is unclear. Some LTPs show
lipid transfer activity between liposomal membranes in
vitro. Others possess antimicrobial activity but are
inactive in lipid transfer. We have purified a protein
called cryoprotectin from cold-acclimated cabbage (Brassica
oleracea L.), that protects thylakoid membranes from
freeze-thaw injury. Amino acid sequencing revealed homology
with the WAX9 family of lipid transfer proteins. In
electrophoretically homogeneous fractions, peptides derived
from at least three LTP isoforms were detected by amino
acid sequencing. To determine which of these proteins were
cryoprotective, we cloned the five known members of the B.
oleracea gene family in E. coli, expressed and purified the
proteins and assayed for lipid transfer and cryoprotection.
WAX9C was expressed poorly and neither LTP activity nor
cryoprotection could be observed up to now. Two of the
isoforms, WAX9B and WAX9E showed lipid transfer activity
but no cryoprotective activity. This confirmed our previous
results with WAX9E isolated from the cuticula of leaves. In
contrast, WAX9A and WAX9D were cryoprotective but showed no
detectable lipid transfer activity. Besides the known lipid
transfer and antimicrobial activities cryoprotection may be
a third function of this versatile class of proteins.
Presented at the XII International Congress on "Genes, Gene
Families and Isozymes" Berlin, 2003