The differential affinity of the usher for chaperone–subunit complexes is required for assembly of complete pili |
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| Authors: | Qinyuan Li Tony W Ng Karen W Dodson Stephane Shu Kin So Ken‐Michael Bayle Jerome S Pinkner Suzanne Scarlata Scott J Hultgren David G Thanassi |
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| Institution: | 1. Center for Infectious Diseases, Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, NY 11794‐5120, USA.;2. Present addresses: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA;3. Department of Molecular Microbiology, Center for Women's Infectious Disease Research, Washington University School of Medicine, St Louis, MO 63110, USA.;4. Massachusetts Institute of Technology, Sloan School of Management, Cambridge, MA 02142, USA;5. New York College of Osteopathic Medicine of New York Institute of Technology, Old Westbury, NY 11568, USA.;6. Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794‐8661, USA. |
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| Abstract: | Attachment to host cells via adhesive surface structures is a prerequisite for the pathogenesis of many bacteria. Uropathogenic Escherichia coli assemble P and type 1 pili for attachment to the host urothelium. Assembly of these pili requires the conserved chaperone/usher pathway, in which a periplasmic chaperone controls the folding of pilus subunits and an outer membrane usher provides a platform for pilus assembly and secretion. The usher has differential affinity for pilus subunits, with highest affinity for the tip‐localized adhesin. Here, we identify residues F21 and R652 of the P pilus usher PapC as functioning in the differential affinity of the usher. R652 is important for high‐affinity binding to the adhesin whereas F21 is important for limiting affinity for the PapA major rod subunit. PapC mutants in these residues are specifically defective for pilus assembly in the presence of PapA, demonstrating that differential affinity of the usher is required for assembly of complete pili. Analysis of PapG deletion mutants demonstrated that the adhesin is not required to initiate P pilus biogenesis. Thus, the differential affinity of the usher may be critical to ensure assembly of functional pilus fibres. |
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