Identification and biochemical characterization of a novel eukaryotic-like Ser/Thr kinase in E. coli

In bacteria, signaling phosphorylation is thought to occur primarily on His and Asp residues. However, phosphoproteomic surveys in phylogenetically diverse bacteria over the past decade have identified numerous proteins that are phosphorylated on Ser and/or Thr residues. Consistently, genes encoding Ser/Thr kinases are present in many bacterial genomes such as E. coli, which encodes at least three Ser/Thr kinases. Here we identify a previously uncharacterized ORF, yegI, and demonstrate that it encodes a novel Ser/Thr kinase. YegI lacks several conserved residues including those important for Mg2+ binding seen in other bacterial Ser/Thr kinases, suggesting that the consensus may be too stringent. We further find that YegI is a two-pass membrane protein with both N- and C-termini located intracellularly.