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Cholesterol Biosynthesis: Pathways and Enzymatic Steps

This presentation delves into the intricate pathways of cholesterol biosynthesis, highlighting key steps such as the condensation of acetyl-CoA, the formation of HMG-CoA, and the subsequent conversion to squalene and lanosterol. We will explore the roles of essential cofactors like NADPH and ATP, and the enzymes involved, including mevalonate kinase and squalene synthase. Additionally, we will discuss the structural transformation from lanosterol to cholesterol and the regulation of these metabolic pathways, providing insights into their biological significance.

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Cholesterol Biosynthesis: Pathways and Enzymatic Steps

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  1. CO2 O C S-CoA O CH3 CH2 2NADPH + H+ C CH3 CH2 COO- COO- C C O O O C C H2 H2 2 NADP+ S-CoA S-CoA O O P P P P Hydroxymethylglutaryl-CoA Irmelin Probst, Walter Storch Vorlesungspräsentation Biochemie Teil 1, SS 2009 Cholesterin - Synthese ADP Pi CH3 CH3 H2 HS-CoA ATP ATP Acetyl-CoA CH2 OH H3C C S-CoA HS-CoA Phospho- mevalonat- kinase Pyrophospho- mevalonat- Decarboxylase Mevalonat- kinase HMG-CoA Synthase Cytosolische Form HMG-CoA Reduktase ß-Keto- thiolase Acetyl-CoA H2 OH Abspaltung von CoA-SH HS-CoA ^ S-CoA Mevalonat = Salz der Mevalonsäure 5-Isopentenyl- pyrophosphat 5-Phosphomevalonat 5-Diphosphomevalonat Reduktion der Carboxylgruppe zur Stufe des Alkohols Acetacetyl-CoA (2 * Acetyl) HMG-CoA Isopreneinheit = aktives Isopren = Baustein aus 5 C-Atomen (C5) ADP ADP

  2. CH3 Isomerisierung CH2 C CH2 CH2 CH2 P O P H2 C P P O O P P - Abspaltung von Pyrophosphat Carbokation O P P Bildung von Squalen aus aktivem Isopren Änderung der Formeldarstellung von 5-Isopentenylpyrophosphat Prenylpyrophosphat Isopentenylpyrophosphat Prenyltransferase + Kondensation von 2 Isopreneinheiten zu C10

  3. P O P + CH2 CH2 CH2 CH2 CH2 P P P P O O O O P P P P P P O O P P - Abspaltung von Pyrophosphat Carbokation CH2 + CH2 CH2 Prenyltransferase Farnesylpyrophosphat (C15) Geranylpyrophosphat (C10) Kondensation mit einem weiteren aktiven Isopren zu C15 Kondensation von 2 Isopreneinheiten zu C10

  4. NADPH +H+ NADP+ P O P H2C Isoprenoide Vit. A Vit. E Ubichinon Kautschuk P O CH2 P P -O P P O- P Squalensynthase Farnesylpyrophosphat Squalen (C30) Kopf an Kopf – Kondensation von 2 Molekülen Farnesylpyrophosphat unter Abspaltung der beiden Pyrophosphatgruppen

  5. Squalen

  6. NADPH +H+ O2 H+ NADP+ H2O + H H CH3 H O CH3 HO H Bildung eines Epoxids H3C CH3 CH3 CH3 Squalenepoxid Squalen CH3 H3C

  7. H3C + CH3 H H CH3 CH3 H+ CH3 H CH3 HO H CH3 H3C Lanosterin

  8. Umwandlung von Lanosterin zu Cholesterin Reduktion der Doppelbindung H3C CH3 CH3 CH3 Umlagerung der Doppelbindung CH3 CH3 HO Entfernung von 3 Methylgruppen H3C CH3 HCOOH + 2 CO2 Cholesterin Lanosterin

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