2Q2H

Crystal structure of the protein secretion chaperone CsaA from Agrobacterium tumefaciens with a genetically fused phage-display derived peptide substrate at the N-terminus.

Summary for 2Q2H

• Entry DOI: 10.2210/pdb2q2h/pdb
• Related: 2Q2I
• Descriptor: Secretion chaperone, phage-display derived peptide, CITRIC ACID, ACETATE ION, ... (4 entities in total)
• Functional Keywords: beta barrel, ob fold, homodimer, chaperone, protein secretion
• Biological source: Agrobacterium tumefaciens str. C58
• Total number of polymer chains: 2
• Total formula weight: 28590.57

Authors

Feldman, A.R.,Shapova, Y.A.,Paetzel, M. (deposition date: 2007-05-28, release date: 2008-04-01, Last modification date: 2023-08-30)

Primary citation

Feldman, A.R.,Shapova, Y.A.,Wu, S.S.,Oliver, D.C.,Heller, M.,McIntosh, L.P.,Scott, J.K.,Paetzel, M.
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, 2008

PubMed 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.

PubMed: 18462752
DOI: 10.1016/j.jmb.2008.03.048

Experimental method

X-RAY DIFFRACTION (1.65 Å)