Feedback regulation of murine pantothenate kinase 3 by coenzyme A and coenzyme A thioesters

Pantothenate kinase catalyzes a key regulatory step in coenzyme A biosynthesis, and there are four mammalian genes that encode isoforms of this enzyme. Pantothenate kinase isoform PanK3 is highly related to the previously characterized PanK1 beta isoform ( 79% identical, 91% similar), and these two almost identical proteins are expressed most highly in the same tissues. PanK1 beta and PanK3 had very similar molecular sizes, oligomeric form, cytoplasmic cellular location, and kinetic constants for ATP and pantothenate. However, these two PanK isoforms possessed distinct regulatory properties. PanK3 was significantly more sensitive to feedback regulation by acetyl- CoA ( IC50 = 1 mu M) than PanK1 beta ( IC50 = 10 mu M), and PanK3 was stringently regulated by long- chain acyl- CoA ( IC50 = 2 mu M), whereas PanK1 beta was not. Domain swapping experiments localized the difference in the two proteins to a 48- amino- acid domain, where they are the most divergent. Consistent with these more stringent regulatory properties, metabolic labeling experiments showed that coenzyme A ( CoA) levels in cells overexpressing PanK3 were lower than in cells overexpressing an equivalent amount of PanK1 beta. Thus, the distinct regulatory properties exhibited by the family of the pantothenate kinases allowed the rate of CoA biosynthesis to be controlled by regulatory signals from CoA thioesters involved in different branches of intermediary metabolism.