Biochemistry I Succinate Dehydrogenase
 
   Electron Transport Pathway:
   Suc & FAD      
   + F2S   
   + F4S, F3S
   CoQ

 FAD Binding (M Chain):
   Load subunit   
   FAD-protein interactions
   FAD Packing
 
  Succinate dehydrogenase converts succinate to fumarate as part of the TCA cycle. It is the only membrane bound enzyme in the TCA cycle. This structure (1FUM.pdb) is the E.coli enzyme with bound FAD and an inhibitor (oxaloacetic acid, OAA). The OAA has been converted to succinate in this illustration. [Note: clicking on the succinate molecule will label it OAA.]

The enzyme complex consists of four separate poly-peptide chains:

  • Chain M (dark blue) contains the bound FAD and substrate binding site.
  • Chain N (Light blue) contains the three iron-sulfur centers.
  • Chains O & P (Green) contain the site for Coenzyme Q.
Suggested viewing:
  1. Overall view: The green subunits are embedded in the membrane, the blue subunits will be in the mitochondrial matrix. The bound FAD is colored as cpk.
  2. Electron Transport Path:
    1. Suc&FAD: A close up view of the substrate next to the FAD, add a surface to see the close contact.
    2. +FeS: Iron-sulfur center closest to the FAD.
      • Zoom: The Fe2S2 Cluster is attached to the enzyme via four Cys residues.
    3. +FS4,F3S: Next two iron-sulfur centers.
    4. Add MQ7:Coenzyme Q-lipophillic electron carrier.
FAD-Protein Interaction: Click to load just the M subunit.
  1. FAD+Suc: Close up view of FAD + substrate with van der Waals surface. Note close contact for electron tranfer.
  2. FAD-proteinInteraction: Specific hydrogen bonds to the adenine, phosphate, and redox part of the FAD. Note the specificity of binding. If you select +/- surface the gold surface is the protein, inside this shell is the FAD, with a grey surface.