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Abstract
Protein kinase A (PrkA), also known as AMP-activated protein kinase, functions as a serine/threonine protein kinase (STPK), has been shown to be involved in a variety of important biologic processes, including pathogenesis of many important diseases in mammals. However, the biological functions of PrkA are less known in prokaryote cells. Here, we explored the function of PrkA as well as its underlying molecular mechanisms using the model bacterium Bacillus subtilis168. When PrkA is inhibited by 9-β-D-arabinofuranosyladenine (ara-A) in the wild type strain or deleted in the ΔprkA mutant strain, we observed sporulation defects in B. subtilis 168, suggesting that PrkA functions as a sporulation-related protein. Transcriptional analysis using the lacZ reporter gene demonstrated that deletion of prkA significantly reduced the expression of the transcriptional factor σK and its downstream genes. Complementation of sigK gene in prkA knockout mutant partially rescued the phenotype of ΔprkA, further supporting the hypothesis that the decreased σK expression should be one of the reasons for the sporulation defect resulting from prkA disruption. Finally, our data confirmed that Hpr (ScoC) negatively controlled the expression of transcriptional factor σK, and thus PrkA accelerated sporulation and the expression of σK by suppression of Hpr (ScoC). Taken together, our study discovered a novel function of the eukaryotic-like STPK PrkA in spore development as well as its underlying molecular mechanism in B. subtilis.
Highlights
Protein phosphorylation is the principal mechanism by which extracellular signals are translated into cellular responses
Effect of Protein kinase A (PrkA) Inhibitor ara-A on Sporulation To determine a possible role of PrkA in B. subtilis, the PrkA inhibitor ara-A was added to decrease the activity of PrkA, and a series of phenotypes, such as vegetative growth, cell morphology, and sporulation were assayed
The significant differences between ara-A-treatment groups and the negative controls suggested that serine/threonine protein kinase (STPK) PrkA in B. subtilis might be involved in sporulation
Summary
Protein phosphorylation is the principal mechanism by which extracellular signals are translated into cellular responses. Recent data from genomic sequencing has further illustrated that the eukaryote-like STPKs exist widely in bacteria, suggesting that this well-characterized protein phosphorylation is distributed in prokaryotes along with two-component systems (Bakal and Davies, 2000). The genome of Mycobacterium tuberculosis contains 11 STPKs (Cole et al, 1998; Av-Gay and Everett, 2000). These STPKs are involved in a variety of processes such as development, cell growth, stress responses, primary and secondary metabolism, biofilm formation, antibiotic resistance, and virulence (Cozzone, 2005; Kristich et al, 2007; Wehenkel et al, 2008; Molle and Kremer, 2010; Ohlsen and Donat, 2010)
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