Histidine mutagenesis of Arabidopsis thaliana pyruvate dehydrogenase kinase.
Pyruvate dehydrogenase kinase ( PDK) is the primary regulator of flux through the mitochondrial pyruvate dehydrogenase complex (PDC). Analysis of the primary amino-acid sequences of PDK from various sources reveals that these enzymes include the five domains characteristic of prokaryotic two-component His-kinases, despite the fact that PDK exclusively phosphorylates Ser residues in the E1alpha subunit of the PDC. This seeming contradiction might be resolved if the PDK-catalyzed reaction employed a phospho-His intermediate. The results from pH-stability studies of autophosphorylated Arabidopsis thaliana PDK did not provide any support for a phospho-His intermediate. Furthermore, site-directed mutagenesis of the two most likely phosphotransfer His residues (H121 and H168) did not abolish either PDK autophosphorylation or the ability to transphosphorylate E1alpha. Thus, PDK is a unique type of protein kinase having a His-kinase-like sequence but Ser-kinase activity.[1]References
- Histidine mutagenesis of Arabidopsis thaliana pyruvate dehydrogenase kinase. Tovar-Mendez, A., Miernyk, J.A., Randall, D.D. Eur. J. Biochem. (2002) [Pubmed]
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