The Predicted Human PANK4 Lacks Key Catalytic Residues for Pantothenate Kinase Function

The human genome is predicted to encode four pantothenate kinase proteins. The PANK1, PANK2, and PANK3 proteins are established functional pantothenate kinases, but the function of the PANK4 protein is disputed. The PANK4 is predicted to encode a fusion of a pantothenate kinase domain at the N‐terminus and a phosphatase domain at the C‐terminus. This putative bifunctional PANK4 is found in the fungi, plant, and animal kingdoms. The plant PANK4 homologue is a functional pantothenate kinase based on its biochemical and genetic characterization. Structural analysis identifies a conserved catalytic glutamate (Glu137 in the human PANK3 protein) as the essential catalytic base for the kinase reaction, while a conserved asparagine (Arg207) forms essential interactions with the pantothenate substrate. While the kinase domain of the human PANK4 has extensive sequence alignment with the human PANK1‐3, the equivalent Glu137 residue in PANK4 is a valine while the equivalent Arg207 residue is a tryptophan. The absence of these two essential catalytic residues suggests that the human PANK4 has lost the pantothenate kinase function. In contrast, the plant PANK4 homologue encodes for the Glu137 and Arg207 residues, consistent with the plant PANK4 homologue indeed functioning as a pantothenate kinase. Bioinformatic analysis showed that the disabling E137V and R207W mutations in the PANK4 protein are conserved in reptiles, birds, and humans (amniotes) while other species in the animal kingdom including amphibians, fish, and insects encode a functional PANK4 protein. These results show that PANK4 experienced conserved, disabling mutations to key catalytic residues during the evolution of amniote. Biochemical experiments will be presented that critically test these bioinformatic predictions concerning the function of the N‐terminal domain of PANK4. The analysis of human PANK4 highlights the importance of confirming bioinformatic predictions with detailed biochemical and structural biology analyses. Support or Funding Information This work was supported in whole or in part by National Institutes of Health Grants GM034496 (to C. O. R.), GM062896 (to S. J.), and Cancer Center Support Grant CA21765 and the American Lebanese Syrian Associated Charities.