PDBsum entry 2q2h

Chaperone

PDB id: 2q2h

Contents

Protein chains

118 a.a. *

106 a.a. *

Ligands

CIT

ACT ×2

Waters ×307

* Residue conservation analysis

PDB id:

2q2h

Name:

Chaperone

Title:

Crystal structure of the protein secretion chaperone csaa from agrobacterium tumefaciens with a genetically fused phage-display derived peptide substrate at the n-terminus.

Structure:

Secretion chaperone, phage-display derived peptide. Chain: a, b. Fragment: fusion protein of a phage-display derived peptide and secretion chaperone protein. Synonym: agr_c_4014p. Engineered: yes

Source:

Agrobacterium tumefaciens str. C58. Organism_taxid: 176299. Strain: c58/atcc 33970. Gene: csaa. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

Resolution:

1.65Å R-factor: 0.161 R-free: 0.173

Authors:

A.R.Feldman,Y.A.Shapova,M.Paetzel

Key ref:

A.R.Feldman et al. (2008). Phage display and crystallographic analysis reveals potential substrate/binding site interactions in the protein secretion chaperone CsaA from Agrobacterium tumefaciens. J Mol Biol, 379, 457-470. PubMed id: 18462752 DOI: 10.1016/j.jmb.2008.03.048

Date:

28-May-07 Release date: 01-Apr-08

Protein chain

A9CI62  (A9CI62_AGRFC) -  Secretion chaperone from Agrobacterium fabrum (strain C58 / ATCC 33970)

Seq: 113 a.a.

Struc: 118 a.a.*

Protein chain

A9CI62  (A9CI62_AGRFC) -  Secretion chaperone from Agrobacterium fabrum (strain C58 / ATCC 33970)

Seq: 113 a.a.

Struc: 106 a.a.

* PDB and UniProt seqs differ at 1 residue position (black cross)

DOI no: 10.1016/j.jmb.2008.03.048

J Mol Biol 379:457-470 (2008)

PubMed id: 18462752

Phage display and crystallographic analysis reveals potential substrate/binding site interactions in the protein secretion chaperone CsaA from Agrobacterium tumefaciens.

A.R.Feldman, Y.A.Shapova, S.S.Wu, D.C.Oliver, M.Heller, L.P.McIntosh, J.K.Scott, M.Paetzel.

ABSTRACT

The protein CsaA has been proposed to function as a protein secretion chaperone in bacteria that lack the Sec-dependent protein-targeting chaperone SecB. CsaA is a homodimer with two putative substrate-binding pockets, one in each monomer. To test the hypothesis that these cavities are indeed substrate-binding sites able to interact with other polypeptide chains, we selected a peptide that bound to CsaA from a random peptide library displayed on phage. Presented here is the structure of CsaA from Agrobacterium tumefaciens (AtCsaA) solved in the presence and absence of the selected peptide. To promote co-crystallization, the sequence for this peptide was genetically fused to the amino-terminus of AtCsaA. The resulting 1.65 A resolution crystal structure reveals that the tethered peptide from one AtCsaA molecule binds to the proposed substrate-binding pocket of a symmetry-related molecule possibly mimicking the interaction between a pre-protein substrate and CsaA. The structure shows that the peptide lies in an extended conformation with alanine, proline and glutamine side chains pointing into the binding pocket. The peptide interacts with the atoms of the AtCsaA-binding pocket via seven direct hydrogen bonds. The side chain of a conserved pocket residue, Arg76, has an "up" conformation when the CsaA-binding site is empty and a "down" conformation when the CsaA-binding site is occupied, suggesting that this residue may function to stabilize the peptide in the binding cavity. The presented aggregation assays, phage-display analysis and structural analysis are consistent with AtCsaA being a general chaperone. The properties of the proposed CsaA-binding pocket/peptide interactions are compared to those from other structurally characterized molecular chaperones.

Selected figure(s)

Figure 1.
Fig. 1. The structure of AtCsaA. (a) A ribbon diagram of dimeric AtCsaA, with molecule A in green and molecule B in pink. (b) A C^α-trace diagram of the superimposed structures of AtCsaA (green), BsCsaA (2NZH, red), and TtCsaA (1GD7, blue). Circles represent areas of the CsaA molecule with high thermal motion. (c) A surface representation of the AtCsaA structure colored according to the negative (red), positive (blue), or neutral (white) electrostatic potential. The location of the putative binding site is indicated with arrows.

Figure 3.
Fig. 3. Structure of the bound peptide from the X15peptide–AtCsaA complex. An electron density omit map calculated for the tethered peptide in the CsaA-binding pocket, contoured at 1 sigma.

The above figures are reprinted by permission from Elsevier: J Mol Biol (2008, 379, 457-470) copyright 2008.

Figures were selected by an automated process.