| Casein kinase I (CKI) enzymes phosphorylate multiple proteins with diverse functions in eukaryotic organisms and may play an important regulatory role in a variety of biological processes. These protein kinases utilize ATP in a reaction forming a phosphate mono-ester that typically can be hydrolyzed by a protein phosphatase. Common features of certain substrates show that CKI activity has an unusual specificity for proteins that are already phosphorylated on an amino acid N-terminal to the site phosphorylated by CKI. Recently, cDNAs encoding several CKI enzymes have been cloned. Sequence analysis reveals that these enzymes constitute a unique family of protein kinases. While their catalytic domains have many similarities, regions outside of this domain vary in length and sequence.;To understand the molecular basis for protein phosphorylation by CKI enzymes, experiments were designed to study the three-dimensional structure of a recombinant mammalian isoform of CKI expressed in Escherichia coli. Crystals of a truncation mutant of CKI... |
