PLANT PHYSIOLOGY , Vol 113, Issue 2 367-376, Copyright © 1997 by American Society of Plant Biologists
|
WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Purification, Characterization, and Structural Analysis of a Plant Low-Temperature-Induced Protein
J. G. Boothe, F. D. Sonnichsen, M. D. de Beus and A. M. Johnson-Flanagan
Department of Agriculture, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5 (J.G.B., M.D.d.B., A.M.J.-F.)
We have purified to near homogeneity a recombinant form of the protein BN28
(rBN28), expressed in response to low temperature in Brassica napus plants,
and we have determined its solution structure. Antibodies raised against
rBN28 were used to characterize the recombinant and native proteins.
Similar to many other low-temperature-induced proteins, BN28 is extremely
hydrophilic, such that it remains soluble following boiling. Immunoblot
analysis of subcellular fractions indicated that BN28 was not strongly
associated with cellular membranes and was localized exclusively within the
soluble fraction of the cell. Contrary to predicted secondary structure
that suggested significant helical content, circular dichroism analysis
revealed that rBN28 existed in aqueous solution largely as a random coil.
However, the helical propensity of the protein could be demonstrated in the
presence of trifluoroethanol. Nuclear magnetic resonance analysis further
showed that rBN28 was in fact completely unstructured (100% coil) in
aqueous solution. Although it had earlier been speculated that BN28-like
proteins from Arabidopsis thaliana might possess antifreeze protein
activity (S. Kurkela and M. Franck [1990] Plant Mol Biol 15: 137-144), no
such activity could be detected in ice recrystallization assays with rBN28.