UK114, a YjgF/Yer057p/UK114 family protein highly conserved from bacteria to mammals, is localized in rat liver peroxisomes Vasily D. Antonenkov a, * , Steffen Ohlmeier a,b , Raija T. Sormunen c , J. Kalervo Hiltunen a a Department of Biochemistry, Biocenter Oulu, University of Oulu, Linnanmaa, P.O. Box 3000, FIN-90014 Oulu, Finland b Proteomics Core Facility of the Biocenter Oulu, Biocenter Oulu, University of Oulu, Linnanmaa, P.O. Box 3000, FIN-90014 Oulu, Finland c Department of Pathology, Biocenter Oulu, University of Oulu, Linnanmaa, P.O. Box 3000, FIN-90014 Oulu, Finland Received 19 March 2007 Available online 30 March 2007 Abstract Mammalian UK114 belongs to a highly conserved family of proteins with unknown functions. Although it is believed that UK114 is a cytosolic or mitochondrial protein there is no detailed study of its intracellular localization. Using analytical subcellular fractionation, electron microscopic colloidal gold technique, and two-dimensional gel electrophoresis of peroxisomal matrix proteins combined with mass spectrometric analysis we show here that a large portion of UK114 is present in rat liver peroxisomes. The peroxisomal UK114 is a soluble matrix protein and it is not inducible by the peroxisomal proliferator clofibrate. The data predict involvement of UK114 in peroxisomal metabolism. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Peroxisomes; UK114; YjgF/Yer057p/UK114 protein family; Clofibrate; Rat liver Mammalian UK114 is a small protein (136 amino acids with a predicted molecular mass of 14.5 kDa, rat protein) forming a homotrimer and expressed predominantly in liver and kidney [1–4]. UK114 belongs to a highly con- served YjgF/Yer057p/UK114 family of proteins with a characteristic C-terminal stretch of amino acid residues. In addition to higher eukaryotes, members of this family have been identified in lower eukaryotes and in bacteria [5–8]. The precise function of UK114 and all proteins in the YjgF/Yer057p/UK114 family remains unknown, although several high-resolution crystal and NMR struc- tures of the family members have been described showing that one subunit folds into pseudo a/b barrel with a nar- row, deep grooves located at the intermonomer surfaces [4,9–12]. Search for functions of the proteins reveals their involvement in such diverse processes as isoleucine biosyn- thesis, translation inhibition, purine metabolism, chaper- one and lipid-binding activities [1,2,5–7,13,14]. The abundance and versatility of the apparent functions led to suggestion that the YjgF/Yer057p/UK114 family mem- bers are implicated in binding and/or degrading of metab- olites, possibly generated in side reactions by central metabolic enzymes [15]. So far the intracellular localization of UK114 has not been investigated in details. Initial studies on mammalian members of the YjgF/Yer057p/UK114 family described them as cytoplasmic components [1–3], though later results indicated a presence of UK114 in mitochondria [7]. Our research on a protein composition of highly purified perox- isomal fractions isolated from rat liver provided initial evi- dence that UK114 might be localized in peroxisomes. Here we present results of a more detailed investigation on the subcellular localization of UK114 indicating that it is a bona fide peroxisomal protein. 0006-291X/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2007.03.136 Abbreviations: BCA, bicinchoninic acid; 2-DE, two-dimensional gel electrophoresis; L-FABP, fatty acid binding protein (liver isoform); PEG, polyethylene glycol; SCP2, sterol carrier protein 2; thiolase, peroxisomal 3-oxoacyl-CoA thiolase. * Corresponding author. Fax: +358 8 553 1141. E-mail address: vasily.antonenkov@oulu.fi (V.D. Antonenkov). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 357 (2007) 252–257