Stabilization of Ribosomal RNA of the Small Subunit by Spermidine in Staphylococcus aureus

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Belinite, Margarita | Khusainov, Iskander | Soufari, Heddy | Marzi, Stefano | Romby, Pascale | Yusupov, Marat | Hashem, Yaser

Edité par CCSD ; Frontiers Media -

International audience. Cryo-electron microscopy is now used as a method of choice in structural biology for studying protein synthesis, a process mediated by the ribosome machinery. In order to achieve high-resolution structures using this approach, one needs to obtain homogeneous and stable samples, which requires optimization of ribosome purification in a speciesdependent manner. This is especially critical for the bacterial small ribosomal subunit that tends to be unstable in the absence of ligands. Here, we report a protocol for purification of stable 30 S from the Gram-positive bacterium Staphylococcus aureus and its cryo-EM structures: in presence of spermidine at a resolution ranging between 3.4 and 3.6 Å and in its absence at 5.3 Å. Using biochemical characterization and cryo-EM, we demonstrate the importance of spermidine for stabilization of the 30 S via preserving favorable conformation of the helix 44.

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