title: Characterization of the plant uncoupling protein, SrUCPA, expressed in spadix mitochondria of the thermogenic skunk cabbage.
abstract: In mammalian brown adipose tissue, uncoupling protein 1 (UCP1), an integral inner mitochondrial membrane protein, triggers a proton leak and converts the energy generated by the resulting electron flow into heat. Although the recent finding of plant UCPs in non-thermogenic tissues has questioned their involvement in thermogenesis, there are few studies of plant UCPs in thermogenic tissues. Therefore, in this work, two cloned UCP cDNAs, SrUCPA and SrUCPB, isolated from the thermogenic spadix of skunk cabbage, were analysed. SrUCPA, not SrUCPB, was identified as the major uncoupling protein, and it was found to be integrated into the inner mitochondrial membrane. Topological analyses indicate that the 1st and 2nd intra-matrix loops are sensitive to trypsin treatment, but the 3rd intra-matrix loop is resistant to it. Using spadix mitochondria, the uncoupling activity of SrUCPA was examined. Although SrUCPA transcripts were constitutively expressed in various tissues irrespective of thermogenic stage, the SrUCPA protein was detected only in the thermogenic tissue or stage. On the other hand, both gene and protein expression for another heat-generating protein, SrAOX, were increased specifically in the thermogenic tissue or stage. Quantitative immunoblot analysis revealed that SrUCPA was an abundant protein in spadix mitochondria, accounting for about 3% of the total mitochondrial protein in the spadix. The results suggest that specific co-expression of SrUCPA and SrAOX protein in the thermogenic tissue or stage, as well as the high expression of SrUCPA protein in spadix mitochondria, may play a role in thermogenesis of skunk cabbage.
authors.affiliation: Cryobiosystem Research Center, Faculty of Agriculture, Iwate University, Morioka, Iwate 020-8550, Japan.
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ito-Inaba
authors.forename: Yamato
authors.initials: Y
authors.lastname: Hida
authors.forename: Megumi
authors.initials: M
authors.lastname: Ichikawa
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kato
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Yamashita
mesh_terms: D029064:Araceae / Q000166:cytology / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019787:Linoleic Acid / Q000494:pharmacology; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D013696:Temperature; D000071256:Uncoupling Protein 1
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; D011687:Purines; D000071256:Uncoupling Protein 1; D019787:Linoleic Acid