StoPK‐1, a serine/threonine protein kinase from the glycopeptide antibiotic producer Streptomyces toyocaensis NRRL 15009, affects oxidative stress response

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Abstract
The glycopeptide antibiotic‐producing bacterium, Streptomyces toyocaensis NRRL 15009, has proteins phosphorylated on Ser, Thr, Tyr and His, implying the presence of a battery of associated kinases. We have identified the Ser/Thr protein kinase gene fragments stoPK‐1, stoPK‐2, stoPK‐3 and stoPK‐4 from S. toyocaensis NRRL 15009 by a polymerase chain reaction (PCR) strategy using oligonucleotide primers based on eukaryotic Ser/Thr and Tyr kinase sequences. One of these (stoPK‐1) was subsequently cloned in its entirety from a 3.2 kb genomic BamHI fragment. stoPK‐1 encodes a 642‐amino‐acid protein with a predicted N‐terminal Ser/Thr kinase domain and a C‐terminal coiled‐coil region divided by a membrane‐spanning region. Expression of StoPK‐1 in Escherichia coli yielded a protein confined to the membrane fraction, which was found to be phosphorylated exclusively on Thr residues and could transfer phosphate to the model substrates myelin basic protein and histone H1. Both autophosphorylation and phosphoryl transfer could be inhibited by the flavanoid apigenin. Disruption of stoPK‐1 with the apramycin resistance gene in the S. toyo‐caensis chromosome resulted in changes in mycelial morphology and an increased sensitivity to the redox cycling agents paraquat and nitrofurantoin on glucose‐containing media. Supplying stoPK‐1 or the S. coelicolor homologue pkaF in trans could reverse this sensitivity, whereas a catalytically inactive mutant of stoPK‐1 could not, indicating that kinase activity is essential for this phenotype. This suggests a link between this membrane‐bound protein kinase in signalling pathways sensitive to oxidative stress and/or glucose metabolism. These results broaden the roles of Ser/Thr protein kinases in bacteria and underscore the diversity of signal transduction mechanisms available to respond to various stimuli.