pH-induced denaturation of proteins: a single salt bridge contributes 3-5 kcal/mol to the free energy of folding of T4 lysozyme.


Abstract

The energetics of a salt bridge formed between the side chains of aspartic acid 70 (Asp70) and histidine 31 (His31) of T4 lysozyme have been examined by nuclear magnetic resonance techniques. The pKa values of the residues in the native state are perturbed from their values in the unfolded protein such that His31 has a pKa value of 9.1 in the native state and 6.8 in the unfolded state at 10 degrees C in moderate salt. Similarly, the aspartate pKa is shifted to a value of about 0.5 in the native state from its value of 3.5-4.0 in the unfolded state. These shifts in pKa show that the salt bridge is stabilized 3-5 kcal/mol. This implies that the salt bridge stabilizes the native state by 3-5 kcal/mol as compared to the unfolded state. This is reflected in the thermodynamic stability of mutants of the protein in which Asp70, His31, or both are replaced by asparagine. These observations and consideration of the thermodynamic coupling of protonation state to folding of proteins suggest a mechanism of acid denaturation in which the unfolded state is progressively stabilized by protonation of its acid residues as pH is lowered below pH 4. The unfolded state is stabilized only if acidic groups in the folded state have lower pKa values than in the unfolded state. When the pH is sufficiently low, the acid groups of both the native and unfolded states are fully protonated, and the apparent unfolding equilibrium constant becomes pH independent. Similar arguments apply to base-induced unfolding.(ABSTRACT TRUNCATED AT 250 WORDS) Study holds ProTherm entries: 3708, 3709, 3710, 14245, 14246 Extra Details: Tm value is for pseudo wild type salt bridge; protonation state; acid groups;,electrostatic contribution

Submission Details

ID: Fi8cuDnc3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:22 p.m.

Version: 1

Publication Details
Anderson DE;Becktel WJ;Dahlquist FW,Biochemistry (1990) pH-induced denaturation of proteins: a single salt bridge contributes 3-5 kcal/mol to the free energy of folding of T4 lysozyme. PMID:2337607
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
102L 1992-09-29T00:00:00+0000 1.74 HOW AMINO-ACID INSERTIONS ARE ALLOWED IN AN ALPHA-HELIX OF T4 LYSOZYME
103L 1992-09-29T00:00:00+0000 1.9 HOW AMINO-ACID INSERTIONS ARE ALLOWED IN AN ALPHA-HELIX OF T4 LYSOZYME
104L 1992-09-29T00:00:00+0000 2.8 HOW AMINO-ACID INSERTIONS ARE ALLOWED IN AN ALPHA-HELIX OF T4 LYSOZYME
107L 1992-12-17T00:00:00+0000 1.8 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME
108L 1992-12-17T00:00:00+0000 1.8 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME
109L 1992-12-17T00:00:00+0000 1.85 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME
110L 1992-12-17T00:00:00+0000 1.7 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME
111L 1992-12-17T00:00:00+0000 1.8 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME
112L 1992-12-17T00:00:00+0000 1.8 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME
113L 1992-12-17T00:00:00+0000 1.8 STRUCTURAL BASIS OF ALPHA-HELIX PROPENSITY AT TWO SITES IN T4 LYSOZYME

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Endolysin P00720 ENLYS_BPT4