2025/04/25 by Rasmus K. Jensen, Liang Xue, Federico Marotta +10 · 1 voice · 3 citations
Biochemistry, Genetics and Molecular Biology · Environmental Science · #Bacterial Genetics and Biotechnology #RNA and protein synthesis mechanisms #Bacteriophages and microbial interactions
paper · pdf · doi:10.1101/2025.04.25.650208
Summary Cryo-electron tomography has emerged as powerful technology for in-cell structural biology, and in combination with breakthroughs in protein structure prediction, offers a unique opportunity for illuminating functions of previously uncharacterized macromolecular complexes. Here, we used the genome-reduced bacterium Mycoplasma pneumoniae as a minimal cell model, and determined in-cell maps of an unknown complex located at the cell surface. By combining proteomics, structure prediction, and bioinformatics, we identified the complex to include the conserved Sec-translocon and an extracellular dome-like structure largely formed by three uncharacterized proteins (Mdps). The Mdps show structural homology to a periplasmic ATP-independent foldase, PrsA, with Mdp444 retaining key catalytic residues. Our study provides the first sub-nanometer resolution maps of the complete bacterial Sec-translocation machinery, depicting several conformational states that allow us to suggest a model for translocation initiation, and revealing its coordination with a novel, extracellular, protein-folding system.