Probing conserved surfaces on PapD

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D L Hung1, S D Knight, S J Hultgren

  • 1Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110, USA.

Molecular Microbiology
|February 27, 1999
PubMed

Insights

PapD, a chaperone protein in Escherichia coli, is essential for assembling P pili. Specific mutations affect its stability and subunit binding, yet Thr-53 is crucial for pilus assembly without impacting chaperone-subunit interactions.

Area of Science:

  • Microbiology
  • Structural Biology
  • Molecular Biology

Background:

  • PapD is a periplasmic chaperone essential for P pilus assembly in pyelonephritic Escherichia coli strains.
  • It belongs to a superfamily of immunoglobulin-like chaperones that, with ushers, assemble adhesive organelles.
  • PapD features two immunoglobulin-like domains separated by a subunit-binding cleft.

Purpose of the Study:

  • To investigate the roles of conserved residue clusters in PapD structure and function.
  • To elucidate the specific contributions of key residues to chaperone stability, subunit binding, and pilus assembly.

Main Methods:

  • Site-directed mutagenesis was employed to alter specific residues within the PapD protein.
  • The effects of these mutations on in vivo stability, chaperone-subunit complex formation, and pilus assembly were assessed.

Main Results:

  • A buried salt bridge within the cleft is critical for PapD's in vivo stability.
  • Residues on the G1 beta strand are essential for efficient subunit binding, aligning with crystal structure data.
  • Mutations at Thr-53, located on the amino-terminal domain surface, are critical for pilus assembly but do not disrupt chaperone-subunit complex formation.

Conclusions:

  • PapD's structure and function are critically dependent on specific conserved residues.
  • While stability and subunit binding are influenced by cleft residues, Thr-53 plays a distinct, essential role in the final pilus assembly step.
  • Understanding these mechanisms provides insights into the assembly of bacterial adhesive organelles.

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