Abstract
The posttranslational modification of proteins with a molecule of phosphate, termed protein phosphorylation, is a mechanism used by cells to regulate cellular activities. Protein phosphorylation occurs in all life forms and is catalyzed by a superfamily of enzymes known as protein kinases. Using bioinformatics, we have identified a family of spore coat protein (Cot) kinases, which are related to the secreted kinase, family with sequence similarity 20C (Fam20C). The founding member of this family is CotH from the spore-forming bacterium Bacillus subtilis. We show that CotH-dependent phosphorylation of the spore proteins CotB and CotG is necessary for the proper germination of spores. Because several CotH-containing organisms are human pathogens, our work has important clinical implications to combat human diseases, such as anthrax.The modification of proteins by phosphorylation occurs in all life forms and is catalyzed by a large superfamily of enzymes known as protein kinases. We recently discovered a family of secretory pathway kinases that phosphorylate extracellular proteins. One member, family with sequence similarity 20C (Fam20C), is the physiological Golgi casein kinase. While examining distantly related protein sequences, we observed low levels of identity between the spore coat protein H (CotH), and the Fam20C-related secretory pathway kinases. CotH is a component of the spore in many bacterial and eukaryotic species, and is required for efficient germination of spores in Bacillus subtilis; however, the mechanism by which CotH affects germination is unclear. Here, we show that CotH is a protein kinase. The crystal structure of CotH reveals an atypical protein kinase-like fold with a unique mode of ATP binding. Examination of the genes neighboring cotH in B. subtilis led us to identify two spore coat proteins, CotB and CotG, as CotH substrates. Furthermore, we show that CotH-dependent phosphorylation of CotB and CotG is required for the efficient germination of B. subtilis spores. Collectively, our results define a family of atypical protein kinases and reveal an unexpected role for protein phosphorylation in spore biology.
