PDBsum entry 4y2o

Structural protein

PDB id: 4y2o

Contents

Protein chains

211 a.a.

142 a.a.

Ligands

PGE ×2

Metals

_NI ×2

Waters ×139

PDB id:

4y2o

Name:

Structural protein

Title:

Structure of cfa/i pili chaperone-major subunit complex (cfaa-cfab)

Structure:

Cfa/i fimbrial subunit a (colonization factor antigen subunit a putative chaperone). Chain: a. Fragment: unp residues 19-238. Engineered: yes. Mutation: yes. Cfa/i fimbrial subunit b. Chain: b. Fragment: unp residues 38-170.

Source:

Escherichia coli o78:h11 (strain h10407 / etec). Organism_taxid: 316401. Strain: h10407 / etec. Gene: cfaa, etec_p948_0390. Expressed in: escherichia coli. Expression_system_taxid: 562. Gene: cfab, etec_p948_0400. Expression_system_taxid: 562

Resolution:

2.42Å R-factor: 0.237 R-free: 0.262

Authors:

R.Bao,D.Xia

Key ref:

R.Bao et al. (2016). Off-pathway assembly of fimbria subunits is prevented by chaperone CfaA of CFA/I fimbriae from enterotoxigenic E. coli. Mol Microbiol, 102, 975-991. PubMed id: 27627030

Date:

10-Feb-15 Release date: 10-Aug-16

Protein chain

No UniProt id for this chain

Struc: 211 a.a.

Protein chain

E3PPC4  (FMC1_ECOH1) -  CFA/I fimbrial subunit B from Escherichia coli O78:H11 (strain H10407 / ETEC)

Seq: 170 a.a.

Struc: 142 a.a.*

* PDB and UniProt seqs differ at 11 residue positions (black crosses)

Mol Microbiol 102:975-991 (2016)

PubMed id: 27627030

Off-pathway assembly of fimbria subunits is prevented by chaperone CfaA of CFA/I fimbriae from enterotoxigenic E. coli.

R.Bao, Y.Liu, S.J.Savarino, D.Xia.

ABSTRACT

The assembly of the class 5 colonization factor antigen I (CFA/I) fimbriae of enterotoxigenic E. coli was proposed to proceed via the alternate chaperone-usher pathway. Here, we show that in the absence of the chaperone CfaA, CfaB, the major pilin subunit of CFA/I fimbriae, is able to spontaneously refold and polymerize into cyclic trimers. CfaA kinetically traps CfaB to form a metastable complex that can be stabilized by mutations. Crystal structure of the stabilized complex reveals distinctive interactions provided by CfaA to trap CfaB in an assembly competent state through donor-strand complementation (DSC) and cleft-mediated anchorage. Mutagenesis indicated that DSC controls the stability of the chaperone-subunit complex and the cleft-mediated anchorage of the subunit C-terminus additionally assist in subunit refolding. Surprisingly, over-stabilization of the chaperone-subunit complex led to delayed fimbria assembly, whereas destabilizing the complex resulted in no fimbriation. Thus, CfaA acts predominantly as a kinetic trap by stabilizing subunit to avoid its off-pathway self-polymerization that results in energetically favorable trimers and could serve as a driving force for CFA/I pilus assembly, representing an energetic landscape unique to class 5 fimbria assembly.