Structural basis of ribosomal RNA repair by RtcB2

Three cryo-EM structures show RtcB2 bound to damaged Escherichia coli 30S subunits, positioning the cleaved 3'-phosphate in its catalytic pocket and capturing GMP-linked intermediates.

• Why it matters: Ribotoxins cleave ribosomal RNA, but the molecular basis for how repair enzymes recognize damaged ribosomes and chemically activate RNA for restoration is unclear.
• What they did: The authors solved three cryo-electron microscopy structures of the RNA ligase RtcB2 with damaged Escherichia coli 30S, including states with enzyme-linked guanosine monophosphate and one with its transfer to RNA.
• The result: RtcB2 reorients during RNA activation, enabling the 5'-hydroxyl-containing RNA segment to enter an adjacent cleft, while comparisons reveal structural barriers to substrate access.

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