Ser/Thr protein kinase PrkC-mediated regulation of GroEL is critical for biofilm formation in Bacillus anthracis

Abstract

PrkC is a conserved Ser/Thr protein kinase encoded in Bacillus anthracis genome. PrkC is shown to be important for B. anthracis pathogenesis, but little is known about its other functions and phosphorylated substrates. Systemic analyses indicate the compelling role of PrkC in phosphorylating multiple substrates, including the essential chaperone GroEL. Through mass spectrometry, we identified that PrkC phosphorylates GroEL on six threonine residues that are distributed in three canonical regions. Phosphorylation facilitates the oligomerization of GroEL to the physiologically active tetradecameric state and increases its affinity toward the co-chaperone GroES. Deletion of prkC in B. anthracis abrogates its ability to form biofilm. Overexpression of native GroEL recovers the biofilm-forming ability of prkC deletion strain. Similar overexpression of GroEL phosphorylation site mutants (Thr to Ala) does not augment biofilm formation. Further analyses indicate the phosphorylation of GroEL in diverse bacterial species. Thus, our results suggest that PrkC regulates biofilm formation by modulating the GroEL activity in a phosphorylation-dependent manner. The study deciphers the molecular signaling events that are important for biofilm formation in B. anthracis.

Intracellular Ser/Thr/Tyr phosphoproteome of the oral commensal Streptococcus gordonii DL1

“…These findings suggest that phosphorylation of enolase may affect cell adhesion during acidic shifts. Regulation of several of the phosphoproteins identified in S. gordonii DL1, such as chaperones DnaK and GroEL, also seem to involve multisite phosphorylation events [30,34,39,63]. This further supports the idea that regulation of cellular activities in prokaryotes is complex and involves integrated patterns of signal transduction.…”

“…In the current study, S. gordonii displayed three phosphorylated molecular chaperones (DnaK, GroEL, tig). Ser/Thr/Tyr phosphorylation has been suggested to activate all these three chaperones in bacteria [27,37,39,52]. By modulating the character and acidity of metabolic end products that accumulate locally, while retaining effective metabolism and other cellular functions at lower environmental pH with the help of ATR responses, cells increase their competitiveness towards less aciduric species [53].…”

A Glimpse Into the Structure and Function of Atypical Type I Chaperonins

“…Interestingly, it has been recently reported that GroEL in pathogenic strain B. anthracis gets phosphorylated and thereby modulates biofilm formation. These findings highlight that phosphorylation of GroEL has functional implications (Arora et al, 2017 ). Acetylation is another post-translational modification associated with E. coli and M. tuberculosis chaperonins, however a functional role has not yet been ascribed to this modification (Liu et al, 2014 ).…”

Clostridium acetobutylicum grows vegetatively in a biofilm rich in heteropolysaccharides and cytoplasmic proteins

“…These proteins are considered to be secreted in a non-classical pathway and some of them (e.g., the GroEL) have been extensively found to moonlight as adhesins and contribute to the biofilm formation [ 32 , 33 , 84 ]. For instance, it was shown that deletion of GroEL-phosphorylating PrkC in Bacillus anthracis abrogated biofilm formation, while overexpression of GroEL led to increased biofilm formation [ 85 , 86 ]. Another intracellular protein abundant in the biofilm is a rubrerythrin encoded by rbr3B (CA_C3597).…”