PDBsum entry 1qpp

Chaperone

PDB id: 1qpp

Contents

Protein chains

207 a.a. *

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Structural basis of chaperone self-Capping in p pilus biogenesis.

Authors

D.L.Hung, J.S.Pinkner, S.D.Knight, S.J.Hultgren.

Ref.

Proc Natl Acad Sci U S A, 1999, 96, 8178-8183. [DOI no: 10.1073/pnas.96.14.8178]

PubMed id

10393968

Abstract

PapD is an immunoglobulin-like chaperone that mediates the assembly of P pili in uropathogenic strains of Escherichia coli. It binds and caps interactive surfaces on pilus subunits to prevent their premature associations in the periplasm. We elucidated the structural basis of a mechanism whereby PapD also interacts with itself, capping its own subunit binding surface. Crystal structures of dimeric forms of PapD revealed that this self-capping mechanism involves a rearrangement and ordering of the C2-D2 and F1-G1 loops upon dimerization which might ensure that a stable dimer is not formed in solution in spite of a relatively large dimer interface. An analysis of site directed mutations revealed that chaperone dimerization requires the same surface that is otherwise used to bind subunits.

Figure 1.
Fig. 1. Structure of the R8A PapD dimer. (A) MOLSCRIPT (33) ribbon drawing of the R8A PapD dimer. The view is looking down the dimer twofold axis. One chaperone subunit is shown in blue and the second subunit in green. In the dimer, contacts between the two N-terminal domains are mediated mostly by the two G1 edge strands across the dimer twofold axis. The interactions between two residues in the C2-D2 loop, Glu-167 and Phe-168, of one subunit with residues Pro-30, Leu-32, Ile-93, Pro-95, and Arg-58 at the lip of the second subunit are shown as ball-and-stick models. (B) Comparison of the C2-D2 loop conformation in monomeric PapD (green) and in the R8A PapD dimer (yellow). The figure was generated after superpositioning of C-terminal domains in monomeric WT PapD and dimeric R8A PapD with an rms deviation of 0.565 Å for 88 C^ atoms.

Figure 4.
Fig. 4. Effect of mutants on chaperone-subunit interactions and chaperone dimerization. (A) Effect of mutations on PapD dimerization. WT PapD, F168R PapD, and G1 strand mutants I105A PapD, I105E PapD, L107A PapD, and L107E PapD were induced for expression 5 min prior to pulse-labeling and then chased for 20 min. Periplasm was isolated from the cells and then subjected to glutaraldehyde crosslinking, and PapD was immunoprecipitated with anti-PapDK antiserum. The immunoprecipitates were subjected to electrophoresis on reducing SDS/12.5% polyacrylamide gels. Triplicate gels of each experiment were quantified as in Fig. 2D. (B) Curve showing the binding of purified WT PapD ( circle ), F168R PapD ( ), native ( ), or alkylated Q108C PapD (IAA-Q108C) ( ) to immobilized MBP/G175-314 protein quantified by ELISA.