17beta-hydroxysteroid dehydrogenase type 8 and carbonyl reductase type 4 assemble as a ketoacyl reductase of human mitochondrial FAS.
Mitochondrial fatty acid synthesis (FAS) generates the octanoyl-group that is required for the synthesis of lipoic acid and is linked to mitochondrial RNA metabolism. All of the human enzymes involved in mitochondrial FAS have been characterized except for beta-ketoacyl thioester reductase (HsKAR), which catalyzes the second step in the pathway. We report here the unexpected finding that a heterotetramer composed of human 17beta-hydroxysteroid dehydrogenase type 8 (Hs17beta-HSD8) and human carbonyl reductase type 4 (HsCBR4) forms the long-sought HsKAR. Both proteins share sequence similarities to the yeast 3-oxoacyl-(acyl carrier protein) reductase (Oar1p) and the bacterial FabG, although HsKAR is NADH dependent, whereas FabG and Oar1p are NADPH dependent. Hs17beta-HSD8 and HsCBR4 show a strong genetic interaction in vivo in yeast, where, only if they are expressed together, they rescue the respiratory deficiency and restore the lipoic acid content of oar1Delta cells. Moreover, these two proteins display a stable physical interaction and form an active heterotetramer. Both Hs17beta-HSD8 and HsCBR4 are targeted to mitochondria in vivo in cultured HeLa cells. Notably, 17beta-HSD8 was previously classified as a steroid-metabolizing enzyme, but our data suggest that 17beta-HSD8 is primarily involved in mitochondrial FAS.
Chen
Zhijun
Z
Biocenter Oulu, and Department of Biochemistry, P. O. Box 3000, FI-90014 University of Oulu, Finland.
Kastaniotis
Alexander J
AJ
Miinalainen
Ilkka J
IJ
Rajaram
Venkatesan
V
Wierenga
Rik K
RK
Hiltunen
J Kalervo
JK
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D000429:Alcohol Oxidoreductases / Q000096:biosynthesis*; D000818:Animals; D064429:Fatty Acid Synthases / Q000096:biosynthesis*; D055786:Gene Knockout Techniques; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D051379:Mice; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D010088:Oxidoreductases; D055503:Protein Multimerization; D011506:Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D008063:Thioctic Acid / Q000378:metabolism
C102228:HSD17B8 protein, human; D024101:Mitochondrial Proteins; D011506:Proteins; D008063:Thioctic Acid; D010088:Oxidoreductases; D015067:17-Hydroxysteroid Dehydrogenases; D000429:Alcohol Oxidoreductases; C021461:beta-ketoacyl thioester reductase; C533692:CBR4 protein, human; D016660:NAD(P)H Dehydrogenase (Quinone); D064429:Fatty Acid Synthases