In-cell discovery and characterization of a non-canonical bacterial protein translocation-folding complex.

In-cell maps reveal a novel bacterial translocation and folding complex involving the Sec-translocon and three uncharacterized proteins in Mycoplasma pneumoniae at sub-nanometer resolution.

• Why it matters: Understanding bacterial protein translocation and folding mechanisms is crucial for insights into cell surface functions and pathogenicity, yet many components remain uncharacterized.
• What they did: Using cryo-electron tomography, proteomics, structure prediction, and integrative modeling, the study mapped the complex's structure and identified three proteins (Mdps) with homology to known foldases, including active Mdp444.
• The result: This work provides the first detailed in-cell structural map of the bacterial Sec-translocation machinery, enabling deeper understanding of co-translational translocation and extracellular protein folding processes.