Experimental Data Snapshot

  • Resolution: 2.30 Å
  • R-Value Free: 0.287 
  • R-Value Work: 0.199 
  • R-Value Observed: 0.199 

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This is version 1.5 of the entry. See complete history


Probing the active site of human manganese superoxide dismutase: the role of glutamine 143.

Hsieh, Y.Guan, Y.Tu, C.Bratt, P.J.Angerhofer, A.Lepock, J.R.Hickey, M.J.Tainer, J.A.Nick, H.S.Silverman, D.N.

(1998) Biochemistry 37: 4731-4739

  • DOI: https://doi.org/10.1021/bi972395d
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    Structural and biochemical characterization of the nonliganding residue glutamine 143 near the manganese of human Mn superoxide dismutase (hMnSOD), a homotetramer of 22 kDa, reveals a functional role for this residue. In the wild-type protein, the side-chain amide group of Gln 143 is about 5 A from the metal and is hydrogen-bonded to Tyr 34, which is a second prominent side chain adjacent to the metal. We have prepared the site-specific mutant of hMnSOD with the conservative replacement of Gln 143 --> Asn (Q143N). The crystal structure of Q143N shows that the side-chain amide nitrogen of residue 143 is 1.7 A more distant from the manganese than in the wild-type enzyme. The Tyr 34 side-chain hydroxyl in Q143N is also moved to become 0.6 A more distant from the metal due to an additional water molecule. Differential scanning calorimetry showed that Q143N is slightly more stable than the wild-type enzyme with Tm for the main unfolding transition increased by 2 degrees C to 90.7 degrees C. Pulse radiolysis and stopped-flow spectrophotometry reveal that unlike wild-type hMnSOD, which is strongly inhibited by peroxide, Q143N MnSOD exhibits no product inhibition even at concentrations of O2. - in the millimolar range, and its catalysis follows Michaelis kinetics with no evidence of cooperativity. However, the overall catalytic activity of this mutant was decreased 2-3 orders of magnitude compared with the wild-type MnSOD, which can account for its lack of product inhibition. Q143N MnSOD lacked the visible absorption spectrum typical of wild-type Mn(III)SOD. Also, unlike the wild-type Mn(III)SOD, which is electron paramagnetic resonance (EPR) silent, Q143N MnSOD has a complex EPR spectrum with many resonances in the region below 2250 G. We conclude that the Gln 143 --> Asn mutation has increased the reduction potential of manganese to stabilize Mn(II), indicating that Gln 143 has a substantial role in maintaining a reduction potential favorable for the oxidation and reduction cycles in the catalytic disproportionation of superoxide. A solvent hydrogen isotope effect near 2 for kcat in catalysis by Q143N hMnSOD indicates rate-contributing proton transfers to form product hydroperoxide anion or hydrogen peroxide. The data demonstrate a prominent role for Gln 143 in maintaining the microenvironment of the manganese and in efficient catalysis of superoxide dismutation to oxygen and hydrogen peroxide.

  • Organizational Affiliation

    Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida 32610, USA.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
198Homo sapiensMutation(s): 1 
UniProt & NIH Common Fund Data Resources
Find proteins for P04179 (Homo sapiens)
Explore P04179 
Go to UniProtKB:  P04179
PHAROS:  P04179
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP04179
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on MN

Download Ideal Coordinates CCD File 
C [auth A],
D [auth B]
Experimental Data & Validation

Experimental Data

  • Resolution: 2.30 Å
  • R-Value Free: 0.287 
  • R-Value Work: 0.199 
  • R-Value Observed: 0.199 
  • Space Group: P 21 21 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 75.5α = 90
b = 78.6β = 90
c = 67.7γ = 90
Software Package:
Software NamePurpose
X-PLORmodel building
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

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Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 1998-01-07
    Type: Initial release
  • Version 1.1: 2008-03-24
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Version format compliance
  • Version 1.3: 2018-04-04
    Changes: Data collection, Other
  • Version 1.4: 2021-11-03
    Changes: Database references, Derived calculations
  • Version 1.5: 2023-08-09
    Changes: Refinement description