title: Effects of COR6.6 and COR15am polypeptides encoded by COR (cold-regulated) genes of Arabidopsis thaliana on dehydration-induced phase transitions of phospholipid membranes.
abstract: Cold acclimation of Arabidopsis thaliana includes the expression of cold-regulated (COR) genes and the accumulation of COR polypeptides. The hydration characteristics of two COR polypeptides, COR6.6 and COR15am, have been determined and their effects on the dehydration-induced liquid crystalline-to-gel and lamellar-to-hexagonal II phase transitions in phospholipid mixtures have been examined. After dehydration at osmotic pressures between 8 and 150 MPa, the water content of the COR polypeptides was less than that of bovine serum albumin, with COr15am the least hydrated: bovine serum albumin > COR6.6 > COR15am. Neither COR6.6 nor COR15am altered the dehydration-induced gel lamellar --> fluid lamellar phase transition temperature of either dipalmitoylphosphatidylcholine or dioleoylphosphatidylcholine (DOPC). In multilamellar vesicles of dioleoylphosphatidylethanolamine:DOPC (1:1, mol:mol) prepared by either freeze-thaw or reverse-phase evaporation methods, neither COR6.6, COR15am, nor bovine serum albumin altered the incidence of the dehydration-induced formation of the inverted hexagonal phase as a function of osmotic pressure. However, a specific ultrastructural alteration--the formation of a striated surface morphology in the lamellar domains--was observed in mixtures of dioleoylphosphatidylethanolamine:DOPC that were dehydrated in the presence of COR15am. Nevertheless, neither COR6.6 nor COR15am appears to participate in a specific protein-phospholipid interaction that alters the dehydration-induced phase behavior of phospholipid vesicles.
authors.affiliation: Department of Soil, Crop and Atmospheric Sciences, Cornell University Ithaca, New York 14853, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Webb
authors.forename: S J
authors.initials: SJ
authors.lastname: Gilmour
authors.forename: M F
authors.initials: MF
authors.lastname: Thomashow
authors.forename: P L
authors.initials: PL
authors.lastname: Steponkus
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins; D003080:Cold Temperature; D005614:Freeze Fracturing; D018506:Gene Expression Regulation, Plant; D006358:Hot Temperature; D008051:Lipid Bilayers; D008854:Microscopy, Electron; D010455:Peptides / Q000235:genetics / Q000502:physiology*; D010743:Phospholipids / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D012710:Serum Albumin, Bovine / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D008051:Lipid Bilayers; D010455:Peptides; D010743:Phospholipids; D010940:Plant Proteins; D014867:Water; C072392:COR6.6 protein, Arabidopsis; D012710:Serum Albumin, Bovine