The ribosome assembly GTPase EngA is involved in redox signaling in cyanobacteria

Abstract

Photosynthetic organisms must cope with environmental challenges, like those imposed by the succession of days and nights or by sudden changes in light intensities, that trigger global changes in gene expression and metabolism. The photosynthesis machinery is particularly susceptible to environmental changes and adaptation to them often involves redox-sensing proteins that are the targets of reactive oxygen species generated by photosynthesis activity. Here we show that EngA, an essential GTPase and ribosome-assembly protein involved in ribosome biogenesis in bacteria and chloroplasts, also plays a role in acclimatization to environmentally relevant stress in Synechococcus elongatus PCC7942 and that PipX, a promiscuous regulatory protein that binds to EngA, appears to fine-tune EngA activity. During growth in cold or high light conditions, the EngA levels rise, with a concomitant increase of the EngA/PipX ratio. However, a sudden increase in light intensity turns EngA into a growth inhibitor, a response involving residue Cys122 of EngA, which is part of the GD1-G4 motif NKCES of EngA proteins, with the cysteine conserved just in the cyanobacteria-chloroplast lineage. This work expands the repertoire of ribosome-related factors transmitting redox signals in photosynthetic organisms and provides additional insights into the complexity of the regulatory interactions mediated by EngA and PipX.

The Signal Transduction Protein PII Controls the Levels of the Cyanobacterial Protein PipX

“…No significant changes in PipX levels of S. elongatus cultures subjected to various conditions of nitrogen, temperature, or light regimes in different studies have been reported [23,40,48]. However, the above-discussed results suggest that transient decreases in PipX levels may occur in response to environmental changes that disrupt PipX-PII complexes.…”

“…Gradient profiling by sequencing (Grad-seq) showed that PipX co-localizes with either metabolic regulators PII, NtcA, and PlmA or with RNA-protein complexes involved in transcription, RNA metabolism, and translation initiation [38]. Last but not least, cyanobacterial synteny [14] led to the identification of the ribosome-assembly GTPase EngA as a PipX regulatory target [39,40], thus providing additional evidence of the regulatory connections between PipX and ribosome function in S. elongatus.…”

Analysing the Cyanobacterial PipX Interaction Network Using NanoBiT Complementation in <em>Synechococcus elongatus</em> PCC7942

“…Gradient profiling by sequencing (Grad-seq) showed that PipX co-localizes with either metabolic regulators PII, NtcA and PlmA or with RNA-protein complexes involved in transcription, RNA metabolism and translation initiation [33]. Synteny analysis in cyanobacteria connected PipX with additional proteins [32] one of which was the ribosome-assembly GTPase EngA, whose binding to PipX and regulatory connections in S. elongatus have already been demonstrated [29,34].…”

Studies on the PII-PipX-NtcA Regulatory Axis of Cyanobacteria Provide Novel Insights into the Advantages and Limitations of Two-Hybrid Systems for Protein Interactions

“…The bacterial two-hybrid system (BACTH), a genetic approach to protein-protein interaction (PPI) based on the reconstitution in E. coli of the adenylate cyclase of Bordetella pertussis from its T18 and T25 domains fused to the proteins of interest [42] has been successfully used to identify components and unravel molecular details of interactions networks involved in cell division or heterocyst patterning in cyanobacteria [43][44][45][46]. We recently used the BACTH system to prove interactions between PipX and the ribosome-assembly GTPase EngA, two proteins whose interactions in cyanobacteria were previously inferred by synteny and in vivo approaches [47,48]. It is worth noting that while BACTH assays gave robust interactions signals between PipX and EngA [49], the Y2H system did not.…”