title: Arabidopsis Cor15am is a chloroplast stromal protein that has cryoprotective activity and forms oligomers.
abstract: Many plants acquire increased freezing tolerance when they are exposed to nonfreezing temperatures of a certain duration. This process is known as cold acclimation and allows plants to protect themselves from freezing injury. A wide variety of polypeptides are induced during cold acclimation, among which is one encoded by COR15A in Arabidopsis (Arabidopsis thaliana). Previous studies showed that the COR15A gene encodes a small, plastid-targeted polypeptide that is processed to a mature form called Cor15am. In this study, we examined the biochemical properties and activities of Cor15am in more detail. We provide evidence that Cor15am localizes almost exclusively to the chloroplast stroma. In addition, the cold-regulated accumulation of Cor15am is affected by chloroplast functionality. Both gel-filtration chromatography and protein cross-linking reveal that Cor15am forms oligomers in the stroma of chloroplasts. Although Cor15am accumulates in response to low temperature, cold acclimation is not a prerequisite for oligomerization of Cor15am. Structural analysis suggests that Cor15am is composed of both ordered and random structures, and can stay soluble with small structural change after boiling and freeze-thaw treatments. Recombinant Cor15am exhibits in vitro cryoprotection of a freeze-labile enzyme, l-lactate dehydrogenase. Furthermore, Cor15am is capable of associating with l-lactate dehydrogenase in vitro and with potential stromal substrates in vivo. On the basis of these results, we propose that Arabidopsis Cor15am is a cryoprotective protein that forms oligomers in the chloroplast stroma, and that direct association of Cor15am with its substrates is part of its cryoprotective mechanism.
authors: The 21st Century Centers of Excellence Program, Cryobiosystem Research Center, Iwate University, Morioka 020-8550, Japan.
authors: Katsuhiro
authors: K
authors: Nakayama
authors: Kumiko
authors: K
authors: Okawa
authors: Tomohiro
authors: T
authors: Kakizaki
authors: Takenori
authors: T
authors: Honma
authors: Hideaki
authors: H
authors: Itoh
authors: Takehito
authors: T
authors: Inaba
mesh_terms: D000064:Acclimatization; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000032:analysis / Q000737:chemistry / Q000502:physiology*; D002736:Chloroplasts / Q000378:metabolism* / Q000502:physiology; D002850:Chromatography, Gel; D005615:Freezing; D007770:L-Lactate Dehydrogenase / Q000378:metabolism / Q000502:physiology; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C116166:COR15 protein, Arabidopsis; D011993:Recombinant Fusion Proteins; D007770:L-Lactate Dehydrogenase