Ribosome hibernation factor promotesStaphylococcalsurvival and differentially represses translation

Abstract

In opportunistic Gram-positive Staphylococcus aureus, a small protein called hibernation-promoting factor (HPFSa) is sufficient to dimerize 2.5-MDa 70S ribosomes into a translationally inactive 100S complex. Although the 100S dimer is observed in only the stationary phase in Gram-negative gammaproteobacteria, it is ubiquitous throughout all growth phases in S. aureus. The biological significance of the 100S ribosome is poorly understood. Here, we reveal an important role of HPFSa in preserving ribosome integrity and poising cells for translational restart, a process that has significant clinical implications for relapsed staphylococcal infections. We found that the hpf null strain is severely impaired in long-term viability concomitant with a dramatic loss of intact ribosomes. Genome-wide ribosome profiling shows that eliminating HPFSa drastically increased ribosome occupancy at the 5′ end of specific mRNAs under nutrient-limited conditions, suggesting that HPFSa may suppress translation initiation. The protective function of HPFSa on ribosomes resides at the N-terminal conserved basic residues and the extended C-terminal segment, which are critical for dimerization and ribosome binding, respectively. These data provide significant insight into the functional consequences of 100S ribosome loss for protein synthesis and stress adaptation.

Disassembly of the Staphylococcus aureus hibernating 100S ribosome by an evolutionarily conserved GTPase

“…We noted that a transposon insertion mutant of hflX (strain NE1325) also phenocopied the in-frame ΔhflX deletion under the same conditions. The S. aureus 100S ribosome is constitutively produced at 37°C throughout all growth phases (3,36). HflX·GTP antagonizes the stability of the 100S ribosome ( Fig.…”

“…The 100S disassembly factor and the exact order of HPF release and 100S splitting have yet to be identified. Furthermore, the Firmicutes 100S ribosomes are constitutively produced from the lag-logarithmic phase through the stationary phase (3,14,36), whereas 100S ribosomes are formed only in cyanobacteria and γ-proteobacteria (including E. coli) during darkness and in the stationary phase (1,9). The molecular basis underpinning the variations in temporal abundance of the 100S ribosome in different bacterial systems has remained elusive.…”

“…The dimerization of 70S ribosomes has been shown to down-regulate translational efficiency in vivo (3) and in vitro (3,14), and bacteria lacking 100S ribosomes are prone to early cell death concomitant with rapid ribosome degradation (3,10,15,16). These studies lead to a model whereby the formation of the 100S complex sequesters the ribosome pool away from active translation, and 70S self-dimerization prevents ribosome degradation by an unknown pathway (3,17). During the stationary phase, the 100S ribosomes are presumably dissociated and reused for new cycles of translation, thereby maintaining cell viability (1,3,16,18).…”

“…These studies lead to a model whereby the formation of the 100S complex sequesters the ribosome pool away from active translation, and 70S self-dimerization prevents ribosome degradation by an unknown pathway (3,17). During the stationary phase, the 100S ribosomes are presumably dissociated and reused for new cycles of translation, thereby maintaining cell viability (1,3,16,18). The process and dissociation factors involved in the reversible transition of silent 100S to a translationally competent 70S ribosome remain poorly understood.…”

“…A common feature of these biological processes is that cells generally conserve energy by undergoing metabolic and translational dormancy because protein synthesis accounts for >50% of energy costs (12,13). The dimerization of 70S ribosomes has been shown to down-regulate translational efficiency in vivo (3) and in vitro (3,14), and bacteria lacking 100S ribosomes are prone to early cell death concomitant with rapid ribosome degradation (3,10,15,16). These studies lead to a model whereby the formation of the 100S complex sequesters the ribosome pool away from active translation, and 70S self-dimerization prevents ribosome degradation by an unknown pathway (3,17).…”