4G39

Mutational analysis of sulfite reductase hemoprotein reveals the mechanism for coordinated electron and proton transfer


Experimental Data Snapshot

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.40 Å
  • R-Value Free: 0.237 
  • R-Value Work: 0.173 
  • R-Value Observed: 0.178 

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This is version 2.0 of the entry. See complete history


Literature

Mutational analysis of sulfite reductase hemoprotein reveals the mechanism for coordinated electron and proton transfer.

Smith, K.W.Stroupe, M.E.

(2012) Biochemistry 51: 9857-9868

  • DOI: https://doi.org/10.1021/bi300947a
  • Primary Citation of Related Structures:  
    4G38, 4G39, 4HTR

  • PubMed Abstract: 

    Sulfite reductase catalyzes the six-electron reduction of sulfite to sulfide. The active site, found in the hemoprotein subunit (SiRHP), sits on the distal face of a negatively charged porphyrinoid called siroheme whose central iron atom is coupled to a proximal Fe(4)S(4) cluster. Four positively charged amino acids are positioned around the active site cavity. Together, these two arginines (R83 and R153) and two lysines (K215 and K217) mitigate the negative charge on the siroheme macrocycle. They also serve as a cage around the distally bound anion that tightens when substrate binds and an active site loop clamps down. Structures of native SiRHP point to these amino acids as being important, but their specific roles are ill-defined. Here, we have altered those four active site amino acids and one amino acid on the flexible loop (N149) to probe their roles in SiRHP activity. None of these positively charged residues is required for electron transfer, but only R83S and N149W variants can produce a fully reduced product. By measuring the electrons used per unit of reduced sulfur released, we show that K215, R153, and K217 are responsible for intermediate and late proton transfers, whereas N149 and R153 play a role in the structure of the flexible loop that controls anion binding and release. R83 is primarily responsible for siroheme binding. Together, the activities and structures of these variants reveal specific roles for each in anion binding and in coupled proton transfer that facilitates electron transfer.


  • Organizational Affiliation

    Department of Biological Science and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.


Macromolecules
Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Sulfite reductase [NADPH] hemoprotein beta-component570Escherichia coli K-12Mutation(s): 1 
Gene Names: b2763cysIJW2733
EC: 1.8.1.2
UniProt
Find proteins for P17846 (Escherichia coli (strain K12))
Explore P17846 
Go to UniProtKB:  P17846
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP17846
Sequence Annotations
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  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Method: X-RAY DIFFRACTION
  • Resolution: 2.40 Å
  • R-Value Free: 0.237 
  • R-Value Work: 0.173 
  • R-Value Observed: 0.178 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 67.598α = 90
b = 77.045β = 90
c = 86.851γ = 90
Software Package:
Software NamePurpose
PHENIXrefinement
SCALEPACKdata scaling
CNSrefinement
DENZOdata reduction
PDB_EXTRACTdata extraction
HKL-2000data collection
CNSphasing

Structure Validation

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Ligand Structure Quality Assessment 


Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2012-12-26
    Type: Initial release
  • Version 1.1: 2013-03-06
    Changes: Database references
  • Version 1.2: 2019-07-17
    Changes: Data collection, Refinement description
  • Version 2.0: 2024-02-28
    Changes: Data collection, Database references, Derived calculations, Non-polymer description, Structure summary