Crystal structure of the heteromolecular chaperone, AscE-AscG, from the type III secretion system in Aeromonas hydrophila

The putative needle complex subunit AscF forms a ternary complex with the chaperones AscE and AscG in the type III secretion system of Aeromonas hydrophila so as to avoid premature assembly. Previously, we demonstrated that the C-terminal region of AscG (residues 62-116) in the hetero-molecular chap...

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Bibliographic Details
Published in:	PloS one 2011-04, Vol.6 (4), p.e19208-e19208
Main Authors:	Chatterjee, Chiradip, Kumar, Sundramurthy, Chakraborty, Smarajit, Tan, Yih Wan, Leung, Ka Yin, Sivaraman, J, Mok, Yu-Keung
Format:	Article
Language:	eng
Subjects:	Aeromonas hydrophila Aeromonas hydrophila - metabolism Amino Acid Sequence Automation Bacterial Proteins - chemistry Biology Chaperones Cloning, Molecular Collaboration Conformation Crystal structure Crystallography Crystallography, X-Ray - methods Crystals Denaturation Disease susceptibility Escherichia coli - metabolism Fines & penalties Helices Hot Temperature Molecular Chaperones - chemistry Molecular Sequence Data Physiology Proteases Protein Binding Protein Conformation Protein denaturation Protein Structure, Secondary Protein Structure, Tertiary Proteins Residues Secretion Structure Temperature Thermal denaturation Thermal stability User interface
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Summary:	The putative needle complex subunit AscF forms a ternary complex with the chaperones AscE and AscG in the type III secretion system of Aeromonas hydrophila so as to avoid premature assembly. Previously, we demonstrated that the C-terminal region of AscG (residues 62-116) in the hetero-molecular chaperone, AscE-AscG, is disordered and susceptible to limited protease digestion. Here, we report the crystal structure of the ordered AscG(1-61) region in complex with AscE at 2.4 Å resolution. Helices α2 and α3 of AscE in the AscE-AscG(1-61) complex assumes a helix-turn-helix conformation in an anti-parallel fashion similar to that in apo AscE. However, in the presence of AscG, an additional N-terminal helix α1 in AscE (residues 4-12) is observed. PscG or YscG in the crystal structures of PscE-PscF-PscG or YscE-YscF-YscG, respectively, assumes a typical tetratricopeptide repeat (TPR) fold with three TPR repeats and one C-terminal capping helix. By comparison, AscG in AscE-AscG(1-61) comprises three anti-parallel helices that resembles the N-terminal TPR repeats in the corresponding region of PscG or YscG in PscE-PscF-PscG or YscE-YscF-YscG. Thermal denaturation of AscE-AscG and AscE-AscG(1-61) complexes demonstrates that the C-terminal disordered region does not contribute to the thermal stability of the overall complex. The N-terminal region of the AscG in the AscE-AscG complex is ordered and assumes a structure similar to those in the corresponding regions of PscE-PscG-PscF or YscE-YscF-YscG complexes. While the C-terminal region of AscG in the AscE-AscG complex is disordered and will assume its structure only in the presence of the substrate AscF. We hypothesize that AscE act as a chaperone of the chaperone to keep AscG in a stable but partially disordered state for interaction with AscF.
ISSN:	1932-6203 1932-6203