Hexaprenyl diphosphate synthase

Hexaprenyl diphosphate synthase (HepPP synthase) is an enzyme that plays a crucial role in the biosynthesis of quinones, which are important for cellular respiration and photosynthesis in many organisms. This enzyme catalyzes the synthesis of hexaprenyl diphosphate (HepPP), a key intermediate in the production of quinones such as ubiquinone (coenzyme Q) and plastoquinone, from isopentenyl diphosphate (IPP) and farnesyl diphosphate (FPP).

Function

Hexaprenyl diphosphate synthase is involved in the isoprenoid biosynthesis pathway, which is essential for the production of a wide range of biomolecules, including vitamins, steroids, and terpenes. The enzyme adds multiple isopentenyl diphosphate units to farnesyl diphosphate to produce hexaprenyl diphosphate. This reaction is crucial for the biosynthesis of quinones, which are involved in electron transport chains in mitochondria and chloroplasts.

Structure

The structure of hexaprenyl diphosphate synthase varies among different species. However, it typically consists of a highly conserved domain that is responsible for the catalytic activity of the enzyme. This domain binds to the substrates, IPP and FPP, and facilitates their condensation to form HepPP. The enzyme's activity is regulated by various factors, including the availability of substrates and the presence of other proteins that can modulate its function.

Clinical Significance

Alterations in the activity of hexaprenyl diphosphate synthase can have significant implications for human health. Given its role in the biosynthesis of coenzyme Q, a deficiency in this enzyme's activity can lead to coenzyme Q10 deficiency, a condition associated with various mitochondrial diseases. Symptoms can include muscle weakness, neurological disorders, and increased susceptibility to oxidative stress.

See Also

• Isoprenoid biosynthesis pathway
• Quinone
• Ubiquinone
• Plastoquinone
• Mitochondrial diseases