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The cavity-chaperone Skp protects its substrate from aggregation but allows independent folding of substrate domains

Walton, Troy A. and Sandoval, Cristina M. and Fowler, C. Andrew and Pardi, Arthur and Sousa, Marcelo C. (2009) The cavity-chaperone Skp protects its substrate from aggregation but allows independent folding of substrate domains. Proceedings of the National Academy of Sciences of the United States of America, 106 (6). pp. 1772-1777. ISSN 0027-8424. PMCID PMC2644113. doi:10.1073/pnas.0809275106.

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Outer membrane proteins (OMPs) of Gram-negative bacteria are synthesized in the cytosol and must cross the periplasm before insertion into the outer membrane. The 17-kDa protein (Skp) is a periplasmic chaperone that assists the folding and insertion of many OMPs, including OmpA, a model OMP with a membrane embedded β-barrel domain and a periplasmic αβ domain. Structurally, Skp belongs to a family of cavity-containing chaperones that bind their substrates in the cavity, protecting them from aggregation. However, some substrates, such as OmpA, exceed the capacity of the chaperone cavity, posing a mechanistic challenge. Here, we provide direct NMR evidence that, while bound to Skp, the β-barrel domain of OmpA is maintained in an unfolded state, whereas the periplasmic domain is folded in its native conformation. Complementary cross-linking and NMR relaxation experiments show that the OmpA β-barrel is bound deep within the Skp cavity, whereas the folded periplasmic domain protrudes outside of the cavity where it tumbles independently from the rest of the complex. This domain-based chaperoning mechanism allows the transport of β-barrels across the periplasm in an unfolded state, which may be important for efficient insertion into the outer membrane.

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Additional Information:© 2009 by The National Academy of Sciences of the USA. Edited by Arthur Horwich, Yale University School of Medicine, New Haven, CT, and approved December 19, 2008 (received for review September 16, 2008). Published online before print January 30, 2009. We thank Lisa Warner for help with NMR data analysis. This work was supported in part by National Science Foundation Grant 0719225 (to M.C.S.) and National Institutes of Health Grant AI033098 (to A.P.). Support for T.A.W was provided by National Institutes of Health Training Grant GM65103. The 800-MHz NMR used in this study was purchased with partial support from National Institutes of Health Grant RR16649, National Science Foundation Grant 0230996, and the W. M. Keck Foundation.
Funding AgencyGrant Number
NIH Predoctoral FellowshipGM65103
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:cavity-based; outer membrane
Issue or Number:6
PubMed Central ID:PMC2644113
Record Number:CaltechAUTHORS:WALpnas09
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13317
Deposited By: Tony Diaz
Deposited On:17 Jul 2009 22:42
Last Modified:08 Nov 2021 22:36

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