Experimental Data Snapshot

  • Resolution: 1.85 Å
  • R-Value Observed: 0.151 

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Contributions of engineered surface salt bridges to the stability of T4 lysozyme determined by directed mutagenesis.

Sun, D.P.Sauer, U.Nicholson, H.Matthews, B.W.

(1991) Biochemistry 30: 7142-7153

  • DOI: https://doi.org/10.1021/bi00243a015
  • Primary Citation of Related Structures:  
    1L37, 1L38, 1L39, 1L40, 1L41

  • PubMed Abstract: 

    Six designed mutants of T4 lysozyme were created in an attempt to create putative salt bridges on the surface of the protein. The first three of the mutants, T115E (Thr 115 to Glu), Q123E, and N144E, were designed to introduce a new charged side chain close to one or more existing charged groups of the opposite sign on the surface of the protein. In each of these cases the putative electrostatic interactions introduced by the mutation include possible salt bridges between residues within consecutive turns of an alpha-helix. Effects of the mutations ranged from no change in stability to a 1.5 degrees C (0.5 kcal/mol) increase in melting temperature. In two cases, secondary (double) mutants were constructed as controls in which the charge partner was removed from the primary mutant structure. These controls proteins indicate that the contributions to stability from each of the engineered salt bridges is very small (about 0.1-0.25 kcal/mol in 0.15 M KCl). The structures of the three primary mutants were determined by X-ray crystallography and shown to be essentially the same as the wild-type structure except at the site of the mutation. Although the introduced charges in the T115E and Q123E structures are within 3-5 A of their intended partner, the introduced side chains and their intended partners were observed to be quite mobile. It has been shown that the salt bridge between His 31 and Asp 70 in T4 lysozyme stabilizes the protein by 3-5 kcal/mol [Anderson, D. E., Becktel, W. J., & Dahlquist, F. W. (1990) Biochemistry 29, 2403-2408]. To test the effectiveness of His...Asp interactions in general, three additional double mutants, K60H/L13D, K83H/A112D, and S90H/Q122D, were created in order to introduce histidine-aspartate charge pairs on the surface of the protein. Each of these mutants destabilizes the protein by 1-3 kcal/mol in 0.15 M KCl at pH values from 2 to 6.5. The X-ray crystallographic structure of the mutant K83H/A112D has been determined and shows that there are backbone conformational changes of 0.3-0.6 A extending over several residues. The introduction of the histidine and aspartate presumably introduces strain into the folded protein that destabilizes this variant. It is concluded that pairs of oppositely charged residues that are on the surface of a protein and have freedom to adopt different conformations do not tend to come together to form structurally localized salt bridges. Rather, such residues tend to remain mobile, interact weakly if at all, and do not contribute significantly to protein stability. It is argued that the entropic cost of localizing a pair of solvent-exposed charged groups on the surface of a protein largely offsets the interaction energy expected from the formation of a defined salt bridge. There are examples of strong salt bridges in proteins, but such interactions require that the folding of the protein provides the requisite driving energy to hold the interacting partners in the correct rigid alignment.

  • Organizational Affiliation

    Department of Physics, University of Oregon, Eugene 97403.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
T4 LYSOZYME164Tequatrovirus T4Mutation(s): 3 
Gene Names: E
Find proteins for P00720 (Enterobacteria phage T4)
Explore P00720 
Go to UniProtKB:  P00720
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP00720
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.85 Å
  • R-Value Observed: 0.151 
  • Space Group: P 32 2 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 61.1α = 90
b = 61.1β = 90
c = 96.9γ = 120
Software Package:
Software NamePurpose

Structure Validation

View Full Validation Report

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1991-10-15
    Type: Initial release
  • Version 1.1: 2008-03-24
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Advisory, Version format compliance
  • Version 1.3: 2017-11-29
    Changes: Derived calculations, Other
  • Version 2.0: 2022-11-23
    Type: Remediation
    Changes: Advisory, Atomic model, Data collection, Database references, Other, Source and taxonomy