Mm. Gonzalez-barroso et al., Structural and functional study of a conserved region in the oncoupling protein UCP1: The three matrix loops are involved in the control of transport, J MOL BIOL, 292(1), 1999, pp. 137-149
It has been reported that the region 261-269 of the uncoupling protein from
brown adipose tissue mitochondria, UCP1, has an important role in the cont
rol of its proton translocating activity. Thus the deletion of residues Phe
267-Lys268-Gly269 leads to the loss of the nucleotide regulation of the pro
tein, while the complete deletion of the segment leads to the formation of
a pore. The region displays sequence homology with the DNA-binding domain o
f the estrogen receptor. The present report analyzes the structure, by NMR
and circular dichroism, of a 20 amino acid residue peptide containing the r
esidues of interest. We demonstrate that residues 263-268 adopt an a-helica
l structure. The helix is at the N-terminal end of the sixth transmembrane
domain. The functional significance of this helix has been examined by site
-directed mutagenesis of the protein expressed recombinantly in yeasts. Alt
erations in the structure or orientation of the region leads to an impairme
nt of the regulation, by nucleotides and fatty acids, of the transport acti
vity. UCP1 is one member of the family formed by the carriers of the mitoch
ondrial inner membrane. The family is characterized by a tripartite structu
re with three repeated segments of about 100 amino acid residues. Two of th
e mutations have also been performed in the first and second matrix loops a
nd the effect on UCP1: function is very similar. We conclude that the three
matrix loops contribute to the formation of the gating domain in UCP1 and
propose that they form a hydrophobic pocket that accommodates the purine mo
iety of the bound nucleotide. (C) 1999 Academic Press.