PDBsum entry 1pv2

Chaperone

PDB id: 1pv2

Contents

Protein chains

241 a.a. *

257 a.a. *

270 a.a. *

Waters ×72

* Residue conservation analysis

References listed in PDB file

Key reference

Title

A new native echsp31 structure suggests a key role of structural flexibility for chaperone function.

Authors

P.M.Quigley, K.Korotkov, F.Baneyx, W.G.Hol.

Ref.

Protein Sci, 2004, 13, 269-277. [DOI no: 10.1110/ps.03399604]

PubMed id

14691241

Abstract

Heat shock proteins and proteases play a crucial role in cell survival under conditions of environmental stress. The heat shock protein Hsp31, produced by gene hchA at elevated temperatures in Escherichia coli, is a homodimeric protein consisting of a large A domain and a smaller P domain connected by a linker. Two catalytic triads are present per dimer, with the Cys and His contributed by the A domain and an Asp by the P domain. A new crystal Form II confirms the dimer and catalytic triad arrangement seen in the earlier crystal Form I. In addition, several loops exhibit increased flexibility compared to the previous Hsp31 dimer structure. In particular, loops D2 and D3 are intriguing because their mobility leads to the exposure of a sizable hydrophobic patch made up by surface areas of both subunits near the dimer interface. The residues creating this hydrophobic surface are completely conserved in the Hsp31 family. At the same time, access to the catalytic triad is increased. These observations lead to the hypothesis for the functioning of Hsp31 wherein loops D2 and D3 play a key role: first, at elevated temperatures, by becoming mobile and uncovering a large hydrophobic area that helps in binding to client proteins, and second, by removing the client protein from the hydrophobic patch when the temperature decreases and the loops adopt their low-temperature positions at the Hsp31 surface. The proposed mode of action of flexible loops in the functioning of Hsp31 may be a general principle employed by other chaperones.

Figure 3.
Figure 3. Comparison of Form I EcHsp31 (top) and Form II EcHsp31 dimer (bottom). Molecular surface of dimers shown with hydrophobic patches in green. Ribbon representation of dimers are shown on the right in the same orientation. Red ribbons in Form I EcHsp31 highlight regions that are disordered in the Form II EcHsp31. Note that the differences (red) between Form I EcHsp31 and Form II EcHsp31 dimer result in the exposure of more hydrophobic regions (green patches) in Form II EcHsp31. These areas are circled in black.

Figure 4.
Figure 4. Molecular surface of Form II EcHsp31 with the linker region from Form I EcHsp31 superimposed to show how Tyr 29 limits access to the active site pocket. The surface of Form II EcHsp31 is colored by domain--A (blue), and P (green), and Cys 185 (yellow). Regions D2 and D3 are modeled in red and orange ball and stick representation from their relative position Form I EcHsp31 structure. Close-up view of the access to Cys 185 of the triad is shown for both Form I and Form II.

The above figures are reprinted by permission from the Protein Society: Protein Sci (2004, 13, 269-277) copyright 2004.