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Structural basis of pilus subunit recognition by the PapD chaperone
M J Kuehn1, D J Ogg, J Kihlberg
1Department of Molecular Microbiology, Washington University, St. Louis, MO 63110.
Science (New York, N.Y.)
|November 19, 1993
Summary
Gram-negative bacteria use periplasmic chaperones like PapD for assembling pili. Researchers determined the crystal structure of PapD with a pilus subunit peptide, revealing key interactions essential for bacterial surface fiber assembly.
Area of Science:
- Microbiology
- Structural Biology
- Bacterial Pathogenesis
Background:
- Gram-negative bacteria assemble virulence-associated pili using periplasmic chaperones.
- PapD is a key chaperone in this process, and its subunit interactions are crucial for pilus assembly.
Purpose of the Study:
- To investigate the structural basis of PapD interactions with pilus subunits.
- To understand the molecular mechanisms underlying pilus assembly in Gram-negative bacteria.
Main Methods:
- X-ray crystallography was used to determine the structure of the PapD chaperone complexed with a pilus subunit peptide.
- Site-directed mutagenesis was employed to validate the role of specific residues in PapD-subunit interactions.
Main Results:
- The crystal structure revealed that a pilus subunit peptide binds to PapD in an extended conformation, with its C-terminus anchored in the chaperone's interdomain cleft.
- Hydrogen bonds to invariant residues Arg8 and Lys112, along with hydrophobic interactions, stabilize the complex.
- Mutations in Arg8 and Lys112 disrupted PapD's ability to bind subunits and mediate pilus assembly in vivo.
Conclusions:
- The determined PapD-peptide structure accurately reflects critical interactions involved in pilus subunit binding.
- Invariant residues Arg8 and Lys112 are essential for PapD function in pilus assembly.
- This structural insight provides a foundation for understanding chaperone-mediated protein assembly in bacteria.