Origin and Evolution of Polycyclic Triterpene Synthesis

Area of Science:

• Biochemistry
• Evolutionary Biology
• Microbiology

Background:

• Polycyclic triterpenes, including hopanoids and sterols, are vital compounds with distinct distributions in bacteria and eukaryotes.
• Sterol biosynthesis was historically considered a eukaryotic innovation, with bacterial sterol presence attributed to horizontal gene transfer.
• Understanding the evolutionary origins of triterpene synthesis is crucial for eukaryogenesis and geobiological biomarker studies.

Purpose of the Study:

• To elucidate the origin and evolution of polycyclic triterpene synthetic pathways.
• To investigate the phylogenetic relationships of key enzymes involved in triterpene biosynthesis.
• To determine the ancestral origins of hopanoid and sterol biosynthesis.

Main Methods:

• Phylogenetic analysis of major triterpene synthesis enzymes.
• Gene neighborhood analysis to infer functional associations.
• Phylogenetic profiling to track gene evolutionary histories.

Main Results:

• The HpnCDE enzyme pathway for squalene biosynthesis appears ancestral in bacteria, originating from carotenoid pathways.
• The Sqs enzyme pathway is linked to horizontal gene transfer and specialized squalene biosynthesis.
• Hopanoid biosynthesis is suggested to be ancient within the Bacteria domain.

Conclusions:

• Bacterial triterpene biosynthesis pathways, particularly hopanoids, are ancestral.
• Eukaryotic sterol biosynthesis likely assembled from ancestral bacterial gene contributions.
• The study reframes the evolutionary narrative of sterols and hopanoids, highlighting bacterial origins.