3DA7

A conformationally strained, circular permutant of barnase


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.25 Å
  • R-Value Free: 0.250 
  • R-Value Work: 0.205 

wwPDB Validation 3D Report Full Report


This is version 1.2 of the entry. See complete history

Literature

Structural and thermodynamic analysis of a conformationally strained circular permutant of barnase.

Butler, J.S.Mitrea, D.M.Mitrousis, G.Cingolani, G.Loh, S.N.

(2009) Biochemistry 48: 3497-3507

  • DOI: 10.1021/bi900039e

  • PubMed Abstract: 
  • Circular permutation of a protein covalently links its original termini and creates new ends at another location. To maintain the stability of the permuted structure, the termini are typically bridged by a peptide long enough to span the original dis ...

    Circular permutation of a protein covalently links its original termini and creates new ends at another location. To maintain the stability of the permuted structure, the termini are typically bridged by a peptide long enough to span the original distance between them. Here, we take the opposite approach and employ a very short linker to introduce conformational strain into a protein by forcing its termini together. We join the N- and C-termini of the small ribonuclease barnase (normally 27.2 A distant) with a single Cys residue and introduce new termini at a surface loop, to create pBn. Compared to a similar variant permuted with an 18-residue linker, permutation with a single amino acid dramatically destabilizes barnase. Surprisingly, pBn is folded at 10 degrees C and possesses near wild-type ribonuclease activity. The 2.25 A X-ray crystal structure of pBn reveals how the barnase fold is able to adapt to permutation, partially defuse conformational strain, and preserve enzymatic function. We demonstrate that strain in pBn can be relieved by cleaving the linker with a chemical reagent. Catalytic activity of both uncleaved (strained) pBn and cleaved (relaxed) pBn is proportional to their thermodynamic stabilities, i.e., the fraction of folded molecules. The stability and activity of cleaved pBn are dependent on protein concentration. At concentrations above approximately 2 microM, cleaving pBn is predicted to increase the fraction of folded molecules and thus enhance ribonuclease activity at 37 degrees C. This study suggests that introducing conformational strain by permutation, and releasing strain by cleavage, is a potential mechanism for engineering an artificial zymogen.


    Organizational Affiliation

    Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.




Macromolecules

Find similar proteins by: Sequence  |  Structure

Entity ID: 1
MoleculeChainsSequence LengthOrganismDetails
Barnase circular permutant
A, B, E, G
111Bacillus amyloliquefaciensMutation(s): 0 
EC: 3.1.27.-
Find proteins for P00648 (Bacillus amyloliquefaciens)
Go to UniProtKB:  P00648
Entity ID: 2
MoleculeChainsSequence LengthOrganismDetails
Barstar
C, D, F, H
90Bacillus amyloliquefaciensMutation(s): 0 
Find proteins for P11540 (Bacillus amyloliquefaciens)
Go to UniProtKB:  P11540
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.25 Å
  • R-Value Free: 0.250 
  • R-Value Work: 0.205 
  • Space Group: P 1
Unit Cell:
Length (Å)Angle (°)
a = 38.879α = 88.10
b = 80.237β = 76.98
c = 81.922γ = 79.47
Software Package:
Software NamePurpose
PDB_EXTRACTdata extraction
HKL-2000data scaling
HKL-2000data reduction
SCALEPACKdata scaling
MOLREPphasing
REFMACrefinement
ADSCdata collection
DENZOdata reduction

Structure Validation

View Full Validation Report or Ramachandran Plots



Entry History 

Deposition Data

Revision History 

  • Version 1.0: 2009-04-14
    Type: Initial release
  • Version 1.1: 2011-07-13
    Type: Version format compliance
  • Version 1.2: 2017-10-25
    Type: Refinement description