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Fragile protein folds: Sequence and environmental factors affecting the equilibrium of two interconverting, stably folded protein conformations.

Authors
  • Xu, Xingjian1, 2
  • Dikiy, Igor1, 3
  • Evans, Matthew R4
  • Marcelino, Leandro P1, 5
  • Gardner, Kevin H1, 5, 6
  • 1 Structural Biology Initiative, CUNY Advanced Science Research Center, New York, NY, USA.
  • 2 Ph.D. Program in Biochemistry, The Graduate Center, CUNY, New York, NY, USA.
  • 3 Current address: Regeneron Pharmaceuticals, Tarrytown, NY, USA.
  • 4 Current address: Acclaim Physician Group, Inc. Fort Worth, TX, USA.
  • 5 Department of Chemistry and Biochemistry, City College of New York, New York, NY, USA.
  • 6 Biochemistry, Chemistry and Biology Ph.D. Programs, The Graduate Center, CUNY, New York, NY, USA.
Type
Published Article
Journal
Magnetic resonance (Gottingen, Germany)
Publication Date
Jan 01, 2021
Volume
2
Issue
1
Pages
63–76
Identifiers
DOI: 10.5194/mr-2-63-2021
PMID: 35603043
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Recent research on fold-switching metamorphic proteins has revealed some notable exceptions to Anfinsen's hypothesis of protein folding. We have previously described how a single point mutation can enable a well-folded protein domain, one of the two PAS (Per-ARNT-Sim) domains of the human ARNT (aryl hydrocarbon receptor nuclear translocator) protein, to interconvert between two conformers related by a slip of an internal β-strand. Using this protein as a test case, we advance the concept of a "fragile fold," a protein fold that can reversibly rearrange into another fold that differs by a substantial number of hydrogen bonds, entailing reorganization of single secondary structure elements to more drastic changes seen in metamorphic proteins. Here we use a battery of biophysical tests to examine several factors affecting the equilibrium between the two conformations of the switching ARNT PAS-B Y456T protein. Of note, we find that factors which impact the HI loop preceding the shifted Iβ-strand affect both the equilibrium levels of the two conformers and the denatured state which links them in the interconversion process. Finally, we describe small molecules that selectively bind to and stabilize the wildtype conformation of ARNT PAS-B. These studies form a toolkit for studying fragile protein folds and could enable ways to modulate the biological functions of such fragile folds, both in natural and engineered proteins.

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