Structural organization and mutational analysis of the human uncoupling protein-2 (hUCP2) gene

Uncoupling proteins (UCPs) are mitochondrial membrane transporters which ar e involved in dissipating the proton electrochemical gradient thereby relea sing stored energy as heat. This implies a major role of UCPs in energy met abolism and thermogenesis which when deregulated are key risk factors for t he development of obesity and other eating disorders. From the three differ ent human UCPs identified so far by gene cloning both UCP2 and UCp3 were ma pped in close proximity (75-150 kb) to regions of human chromosome 11 (11q1 3) that have been linked to obesity and hyperinsulinaemia. At the amino aci d level hUCP2 has about 55% identity to hUCP1 while hUCP3 is 71% identical to hUCP2. In this study we have deduced the genomic structure of the human UCP2 gene by PCR and direct sequence analysis. The hUCP2 gene spans over 8. 7 kb distributed on 8 exons. The localization of the exon/intron boundaries within the coding region matches precisely that of the hUCP1 gene and is a lmost conserved in the recently discovered hUCP3 gene as well. The high deg ree of homology at the nucleotide level and the conservation of the exon/in tron boundaries among the three UCP genes suggests that they may have evolv ed from a common ancestor or are the result from gene duplication events. M utational analysis of the hUCP2 gene in a cohort of 172 children (aged 7-13 ) of Caucasian origin revealed a polymorphism in exon 4 (C to T transition at position 164 of the cDNA resulting in the substitution of an alanine by a valine at codon 55) and an insertion polymorphism in exon 8. The insertio n polymorphism consists of a 45 bp repeat located 150 bp downstream of the stop codon in the 3'-UTR. The allele frequencies were 0.63 and 0.37 for the alanine and valine encoded alleles, respectively, and 0.71 versus 0.29 for the insertion polymorphism. The allele frequencies of both polymorphisms w ere not significantly elevated in a subgroup of 25 children characterized b y low Resting Metabolic Rates (RMR). So far a direct correlation of the obs erved genotype with (RMR) and Body Mass Index (BMI) was not evident. Expres sion studies of the wild type and mutant forms of UCP2 should clarify the f unctional consequences these polymorphisms may have on energy metabolism an d body weight regulation. (C) 1998 Elsevier Science Inc.