First published online January 23, 2003; 10.1104/pp.015891
Plant Physiol, March 2003, Vol. 131, pp. 963-975
Conformation of a Group 2 Late Embryogenesis Abundant Protein
from Soybean. Evidence of Poly (L-Proline)-type II
Structure1
Jose L.
Soulages,
Kangmin
Kim,2
Estela L.
Arrese,
Christina
Walters, and
John C.
Cushman*
Department of Biochemistry and Molecular Biology, 355 Noble
Research Center, Oklahoma State University, Stillwater, Oklahoma
74078-0454 (J.L.S., E.L.A.); Department of Biochemistry, MS200, 311B
Fleischmann Agriculture, University of Nevada, Reno, Nevada 89557-0014
(K.K., J.C.C.); and National Center for Germplasm Resources
Preservation, U.S. Department of Agriculture-Agricultural Research
Service, Fort Collins, Colorado 80523 (C.W.)
Late embryogenesis abundant (LEA) proteins are members of a large
group of hydrophilic, glycine-rich proteins found in plants, algae,
fungi, and bacteria known collectively as hydrophilins that are
preferentially expressed in response to dehydration or hyperosmotic
stress. Group 2 LEA (dehydrins or responsive to abscisic acid) proteins
are postulated to stabilize macromolecules against damage by freezing,
dehydration, ionic, or osmotic stress. However, the structural and
physicochemical properties of group 2 LEA proteins that account for
such functions remain unknown. We have analyzed the structural
properties of a recombinant form of a soybean (Glycine max) group 2 LEA (rGmDHN1). Differential scanning calorimetry of purified rGmDHN1 demonstrated that the protein does not display a
cooperative unfolding transition upon heating. Ultraviolet absorption and circular dichroism spectroscopy revealed that the protein is in a
largely hydrated and unstructured conformation in solution. However,
ultraviolet absorption and circular dichroism measurements collected at
different temperatures showed that the protein exists in equilibrium
between two extended conformational states: unordered and left-handed
extended helical or poly (L-proline)-type II structures. It
is estimated that 27% of the residues of rGmDHN1 adopt or poly (L-proline)-type II-like helical conformation at 12°C.
The content of extended helix gradually decreases to 15% as the
temperature is increased to 80°C. Studies of the conformation of the
protein in solution in the presence of liposomes, trifluoroethanol, and sodium dodecyl sulfate indicated that rGmDHN1 has a very low intrinsic ability to adopt  -helical structure and to interact with
phospholipid bilayers through amphipathic -helices. The ability of
the protein to remain in a highly extended conformation at low
temperatures could constitute the basis of the functional role of
GmDHN1 in the prevention of freezing, desiccation, ionic, or osmotic
stress-related damage to macromolecular structures.
1
This work was supported in part by the U.S.
Department of Agriculture National Research Initiative-Competitive
Grants Program (grant no. 98-35100-10216 to J.C.C.), by the National
Institutes of Health (grant no. GM 55622 to J.L.S.), and by the Nevada
Agricultural Experiment Station (publication no. 0302382).
2
Present address: 193 E.R. Madigan Laboratory, 1201 W. Gregory Avenue, Urbana, IL 61801.
*
Corresponding author; e-mail jcushman{at}unr.edu;
fax 775-784-1650.
© 2003 American Society of Plant Biologists
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