Binding Thermodynamics of Statins to HMGCoA Reductase

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Binding Thermodynamics of Statins to HMG-CoA
Reductase

• Presented by Ashley Mericle

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Statins

• Work in the liver1 and are used to lower
  cholesterol levels
• most effective at lowering the LDL (Low-density
  lipoprotein) bad cholesterol, but also have
  some effect on lowering triglycerides and raising
  HDL (High-density lipoprotein) good
  cholesterol1
• inhibit the enzyme that catalyzes the
  rate-limiting step in the synthesis of
  cholesterol

• HMG-CoA 2NADPH 2H
  mevalonate 2NADP CoASH

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Structure

• All statins have a common part and a variable
  hydrophobic region.
• Type I and Type II

Variable hydrophobic region
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Pravastatin

• Type I statin
• Pravachol1

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Fluvastatin

• Type II statin
• Lescol1

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Cerivastatin

• Type II statin
• Exhibited fatal side effects which led to its
  withdrawal in 2001

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Atorvastatin

• Type II statin
• Lipitor 1

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Rosuvastatin

• Type II statin
• Crestor1

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Side Effects

• beneficial anti-inflammatory properties and
  plaque stabilization
• Some exhibit fatal side effects

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Methods Statin Purification

• The 5 statins were purified from commercial pills
  using reverse-phase high-pressure liquid
  chromatography.

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Methods Enzymatic Assays

• Assays were performed in 100 mM sodium phosphate
  buffer.
• HMG-CoA Km, NADPH Km, and inhibition constant
  (Ki) were all determined through the assays.

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Methods Isothermal Titration Calorimetry

• Isothermal titration calorimetry experiments were
  carried out.
• The binding enthalpies were determined.

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Results Enzyme Characterization

• Statins are competitive inhibitors with respect
  to HMG-CoA, but not NADPH.

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Results Enzyme Inhibition Experiments

• The inhibition constant, Ki, for each of the
  statins was determined by measuring the decrease
  in catalytic activity with an increase the
  concentration of the inhibitor.

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Inhibition Constant Results
Normalized initial velocity vs. statin
concentration
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References

• 1(2007 October 18). American Heart Association.
  Retrieved February 19, 2008, from
  Cholesterol-Lowering Drugs Web site
  http//www.americanheart.org/presenter.jhtml?ident
  ifier163