1. Cloning and functional characterization of an uncoupling protein homolog in hummingbirds.
- Author
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Vianna CR, Hagen T, Zhang CY, Bachman E, Boss O, Gereben B, Moriscot AS, Lowell BB, Bicudo JE, and Bianco AC
- Subjects
- Amino Acid Sequence, Animals, Birds physiology, Cloning, Molecular, Ion Channels, Membrane Potentials, Mitochondria physiology, Molecular Sequence Data, Phylogeny, RNA, Messenger biosynthesis, Saccharomyces cerevisiae physiology, Sequence Homology, Amino Acid, Thermogenesis, Tissue Distribution, Uncoupling Protein 1, Uncoupling Protein 2, Uncoupling Protein 3, Birds genetics, Carrier Proteins genetics, Membrane Proteins genetics, Membrane Transport Proteins, Mitochondrial Proteins, Proteins genetics
- Abstract
The cDNA of an uncoupling protein (UCP) homolog has been cloned from the swallow-tailed hummingbird, Eupetomena macroura. The hummingbird uncoupling protein (HmUCP) cDNA was amplified from pectoral muscle (flight muscle) using RT-PCR and primers for conserved domains of various known UCP homologs. The rapid amplification of cDNA ends (RACE) method was used to complete the cloning of the 5' and 3' ends of the open reading frame. The HmUCP coding region contains 915 nucleotides, and the deduced protein sequence consists of 304 amino acids, being approximately 72, 70, and 55% identical to human UCP3, UCP2, and UCP1, respectively. The uncoupling activity of this novel protein was characterized in yeast. In this expression system, the 12CA5-tagged HmUCP fusion protein was detected by Western blot in the enriched mitochondrial fraction. Similarly to rat UCP1, HmUCP decreased the mitochondrial membrane potential as measured in whole yeast by uptake of the fluorescent potential-sensitive dye 3',3-dihexyloxacarbocyanine iodide. The HmUCP mRNA is primarily expressed in skeletal muscle, but high levels can also be detected in heart and liver, as assessed by Northern blot analysis. Lowering the room's temperature to 12-14 degrees C triggered the cycle torpor/rewarming, typical of hummingbirds. Both in the pectoral muscle and heart, HmUCP mRNA levels were 1.5- to 3.4-fold higher during torpor. In conclusion, this is the first report of an UCP homolog in birds. The data indicate that HmUCP has the potential to function as an UCP and could play a thermogenic role during rewarming.
- Published
- 2001
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