In most bacteria, protein biosynthesis is suppressed by the formation of 100S ribosome, a dimmer of 70S ribosomes, under the starvation stress. In the case of gram-negative bacteria such as Escherichia coli, the 100S ribosome is promoted by ribosome modulation factor (RMF) and hibernation promoting factor (HPF) binding to 70S ribosomes. To understand the mechanisms of the suppression of the protein biosynthesis, we tried to analyze the structure by cryo-EM.
The 11,889 particle images of the 100S ribosome were used for structural analysis. We treated the images of the two 70S ribosomes individually for 3D image reconstruction and analyzed the structure. The structure of 70S ribosome with part of its partner on the 100S ribosome was solved at 18 Å. The model of the 100S ribosome was build by using the density map. We revealed that the ribosomal protein S2 interact with S3 and S5 in 30S subunit of its partner.
Recently, we solved the structure of 100S ribosome from Staphylococcus aureus which is gram-positive bacteria. The formation of 100S ribosome is promoted by HPF homolog (named SaHPF). We observed 100S ribosome from S. aureus. Surprisingly, the binding formation of two 70S ribosomes from S. aureus is completely different to E. coli’s one. I will discuss about the difference between 100S ribosome and difference of survival strategy under the stress condition between gram-negative and positive bacteria.