Comparative analysis of human and murine Uncoupling Protein 1 reveals essential structural features of human UCP1

Background: Mitochondrial uncoupling protein 1 (UCP1) is a unique protein of brown adipose tissue. Upon activation by free fatty acids, UCP1 facilitates a thermogenic net proton flux across the mitochondrial inner membrane. Non-complexed purine nucleotides inhibit this fatty acid-induced activity of UCP1. By far the most available data have been generated from rodent model systems. In the light of being a putative pharmacological target for the treatment of metabolic disease, specific aspects of human UCP1 function and its comparability to rodent orthologues are of importance. Methods: In the present study, we established a doxycycline-regulated cell model with inducible human or murine UCP1 expression and conducted functional studies using respirometry. Results: We demonstrate that human and murine UCP1 exhibit similar specific fatty acid-induced activity, but divergent inhibitory potential of purine nucleotides. Mutagenesis of non-conserved residues in human UCP1 revealed structural components in α-helix 56 and α-helix 6 crucial for uncoupling function. Conclusions: A deeper structure-function analysis of UCP1 is not only essential to understand its unique function but is also needed in the search for new UCP1 activators.