The uncoupling protein UCP1 is a member of a superfamily of homologous proteins formed by the
mitochondrial metabolite transporters.
Function
Their are three types of adipose tissue: White adipose tissue (WAT), Brown Adipose tissue (BAT) and Beige (a combination of WAT and BAT). BAT and Beige are both thermogenic, meaning that it can generate heat when it's cold or when the body has excess energy.
Both types of thermogenic adipocytes can increase energy expenditure through the uncoupling of oxidative metabolism from ATP synthesis, releasing energy as heat. This property is conferred by the presence of a unique protein, uncoupling protein 1 (UCP1), also known as thermogenin. In most cells lacking UCP1, proton gradient that has been generated via the electron transport chain can only be dissipated through ATP formation by complex V (ATP synthase). UCP1 is located in the inner mitochondrial membrane and catalyzes a proton leak across the inner membrane. As a result of this process, fuel oxidation in brown adipocytes becomes uncoupled from ATP synthesis, and energy is dissipated as heat.
Mature brown adipocytes have multilocular appearance, due to the fact that they contain numerous small lipid droplets (LDs), surrounded by a large number of mitochondria. BAT is characterized by rich blood and nerve supply. The adaptive thermogenic response of BAT, driven by the sympathetic nervous system; norepinephrine (NE) released by sympathetic nerves act on β-adrenergic receptors, initiates signaling cascades for triglycerides hydrolysis (via activation of hormone sensitive lipase). The released fatty acids from LDs activate UCP1, and are oxidized to serve as an energy source of thermogenesis.
Disease
Knockout of the UCP1 gene produces mice that are cold intolerant.
Relevance
If we could increase UCP1's expression, it may effect energy balance towards energy expenditure and lead to wheight loss. It is especially important in this age in which the obecity phenomenon is expanding.
Structural highlights
UCP1 is composed of three repeated domains of approximately 100 amino acids each.
Its activity is regulated by purine nucleotides (inhibitors) and non-esterified fatty acids (activators).
It proposes that in the protein core there must exist a hydrophilic translocation pore whose access is controlled by gates. It is highly likely that the hydrophilic channel is formed by the transmembrane á-helices and that loops contribute to the formation of the gates.
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