Effect of salt on the urea-unfolded form of barstar probed by m value measurements.


Abstract

To probe for residual structure present in the urea-unfolded form of the small protein barstar, to determine how salt might modulate such structure, and to determine how such structure might affect the stability of the protein, mutant variants that display m values different from that of the wild-type protein have been studied. The mutant proteins were obtained by site-directed mutagenesis at residue positions located on the surface of the folded protein. The m value, which represents the preferential free energy of interaction of urea with the unfolded form in comparison to that with the folded state, was determined from equilibrium urea-induced unfolding curves. Mutant proteins for which the m values were significantly greater than (m(+) mutant forms), significantly smaller than (m(-) mutant forms), or similar to (m(0) mutant forms) the m value determined for the wild-type protein were studied. The unfolded forms of the m(0), m(+) and m(-) mutant proteins represent different components within the unfolded form ensemble, which differ from each other in their solvent-exposed surface areas. Hence, the m value has been used as a measure of residual structure in the unfolded form. To further understand the nature of structures present in the unfolded form ensemble, the effects of the salt KCl on the stabilities of the wild-type and the mutant proteins, as well as on the structures present in the unfolded form ensemble, were also studied. It was found that the m values of the m(0), m(+) and m(-) mutant proteins all converge to the wild-type m value in the presence of KCl. This result indicates that the salt modulates residual structure in the unfolded form by screening electrostatic interactions that maintain compact and expanded components in the unfolded protein ensemble. The use of free energy cycles has allowed the effect of salt on the structure and free energy of the unfolded protein to be related to the stability of the protein. Study holds ProTherm entries: 17167, 17168, 17169, 17170, 17171, 17172, 17173, 17174, 17175, 17176, 17177, 17178, 17179, 17180, 17181, 17182, 17183, 17184, 17185, 17186, 17187, 17188, 17189, 17190, 17191, 17192, 17193, 17194, 17195, 17196, 17197, 17198, 17199 Extra Details: 250 microM EDTA and 250 microM DTT were added in the experiment. salt; m value; solvent-exposed surface areas; electrostatic interactions

Submission Details

ID: gCCyMriS3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:49 p.m.

Version: 1

Publication Details
Pradeep L;Udgaonkar JB,Biochemistry (2004) Effect of salt on the urea-unfolded form of barstar probed by m value measurements. PMID:15350126
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P
 

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)


Relevant PDB Entries

Structure ID Release Date Resolution Structure Title
1BTA 1994-07-31 THREE-DIMENSIONAL SOLUTION STRUCTURE AND 13C ASSIGNMENTS OF BARSTAR USING NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
1AB7 1997-09-04 NMR 15N RELAXATION AND STRUCTURAL STUDIES REVEAL CONFORMATIONAL EXCHANGE IN BARSTAR C40/82A, 30 STRUCTURES
1BTB 1994-07-31 THREE-DIMENSIONAL SOLUTION STRUCTURE AND 13C ASSIGNMENTS OF BARSTAR USING NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY
1L1K 2002-12-04 NMR Identification and Characterization of the Flexible Regions in the 160 KD Molten Globule-like Aggregate of Barstar at Low pH
2ZA4 2008-05-20 1.58 Crystal Structural Analysis of Barnase-barstar Complex
1AY7 1999-03-02 1.7 RIBONUCLEASE SA COMPLEX WITH BARSTAR
1B2S 1998-12-08 1.82 STRUCTURAL RESPONSE TO MUTATION AT A PROTEIN-PROTEIN INTERFACE
1X1Y 2005-04-26 1.9 Water-mediate interaction at aprotein-protein interface
1BRS 1994-06-22 2.0 PROTEIN-PROTEIN RECOGNITION: CRYSTAL STRUCTURAL ANALYSIS OF A BARNASE-BARSTAR COMPLEX AT 2.0-A RESOLUTION
2HXX 2006-08-22 2.0 Aminotryptophan Barstar
1B27 1998-12-09 2.1 STRUCTURAL RESPONSE TO MUTATION AT A PROTEIN-PROTEIN INTERFACE
1X1W 2005-04-26 2.1 Water-mediate interaction at aprotein-protein interface
1B2U 1998-12-09 2.1 STRUCTURAL RESPONSE TO MUTATION AT A PROTEIN-PROTEIN INTERFACE
3DA7 2009-04-14 2.25 A conformationally strained, circular permutant of barnase
1X1U 2005-04-26 2.3 Water-mediate interaction at aprotein-protein interface
1X1X 2005-04-26 2.3 Water-mediate interaction at aprotein-protein interface
1B3S 1998-12-09 2.39 STRUCTURAL RESPONSE TO MUTATION AT A PROTEIN-PROTEIN INTERFACE
1BGS 1994-04-30 2.6 RECOGNITION BETWEEN A BACTERIAL RIBONUCLEASE, BARNASE, AND ITS NATURAL INHIBITOR, BARSTAR
1A19 1998-04-08 2.76 BARSTAR (FREE), C82A MUTANT

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Barstar P11540 BARS_BACAM