Mycoplasma pneumoniae J‐domain protein required for terminal organelle function

Summary The cell wall‐less prokaryote Mycoplasma pneumoniae causes tracheobronchitis and primary atypical pneumonia in humans. Colonization of the respiratory epithelium requires proper assembly of a complex, multifunctional, polar terminal organelle. Loss of a predicted J‐domain protein also having domains unique to mycoplasma terminal organelle proteins (TopJ) resulted in a non‐motile, adherence‐deficient phenotype. J‐domain proteins typically stimulate ATPase activity of Hsp70 chaperones to bind nascent peptides for proper folding, translocation or macromolecular assembly, or to resolve stress‐induced protein aggregates. By Western immunoblotting all defined terminal organelle proteins examined except protein P24 remained at wild‐type levels in the topJ mutant; previous studies established that P24 is required for normal initiation of terminal organelle formation. Nevertheless, terminal organelle proteins P1, P30, HMW1 and P41 failed to localize to a cell pole, and when evaluated quantitatively, P30 and HMW1 foci were undetectable in >40% of cells. Complementation of the topJ mutant with the recombinant wild‐type topJ allele largely restored terminal organelle development, gliding motility and cytadherence. We propose that this J‐domain protein, which localizes to the base of the terminal organelle in wild‐type M. pneumoniae, functions in the late stages of assembly, positioning, or both, of nascent terminal organelles.