The Mevalonate Pathway is a necessary pathway that occurs in archaea, eukaryotes and select bacteria. It has mainly been studied with regard to cholesterol biosynthesis and how it relates to cardiovascular disease in humans, but has recently garnered attention for its many other essential roles within human pathology. The pathway begins in the cytoplasm with acetyl-CoA and acetoacetyl-CoA, which interact with acetyl-CoA acetyltransferase, coenzyme A and water to synthesize hydroxymethylglutaryl-CoA synthase. In turn, this synthase teams up with coenzyme A and a hydrogen ion in the endoplasmic reticulum to create 3-hydroxy-3-methylglutaryl-CoA. 3-Hydroxy-3-methylglutaryl-CoA then pairs with 2NADPH, 2 hydrogen ions and is catalyzed by 3-hydroxy-3-methylglutaryl-coenzyme A reductase to produce (R)-mevalonate, also producing byproducts CoA and NADP. Exiting the endoplasmic reticulum, and entering the peroxisome, (R)-mevalonate uses the help of ATP and mevalonate kinase to create mevalonic acid (5P). This piece is especially important to the human species as decreased activity of the enzyme mevalonate kinase has been found to be a direct link to two auto-inflammatory disorders: MVA and HIDS. Using phosphomevalonate kinase and ATP, the pathway re-enters the cytoplasm and mevalonic acid (5P) converts to (R)-mevalonic acid-5-pyrophosphate and ADP. (R)-mevalonic acid-5-pyrophosphate, ATP and diphosphomevalonate decarboxylase work together to create phosphate, carbon dioxide, ADP and isopentenyl pyrophosphate. Re-entering the peroxisome, isopentenyl diphosphate delta isomerase 1 is waiting to propel isopentenyl pyrophosphate into dimethylallylpyrophosphate. This pushes the pathway back into the cytoplasm, where another isopentenyl pyrophosphate molecule and the enzyme farnesyl pyrophosphate synthase create pyrophosphate and geranyl-PP. Yet another isopentenyl pyrophosphate molecules works with farnesyl pyrophosphate synthase to produce pyrophosphate and farnesyl pyrophosphate. Now in the endoplasmic reticulum membrane, 2 farnesyl pyrophosphate molecules with the help of NADPH and a hydrogen ion catalyze with squalene synthase and create squalene. This is an important first step in the specific hepatic cholesterol pathway. Remaining in the endoplasmic reticulum membrane, squalene, FMNH, oxygen and squalene monooxygenase synthesize (S)-2,3-epoxysqualene. This comes along with the byproducts of flavin mononucleotide, a hydrogen ion and water. In the final reaction within this pathway, lanesterol synthase converts (S)-2,3-epoxysqualene to lanosterin. Not pictured in this pathway, lanosterin will eventually be converted to cholesterol, an important part of many functions in the human body.

Mevalonate Pathway References