Existence and implications of hop-17(21)-enes in the lower Cretaceous of the Saihantala Sag, Erlian Basin, China

C31- to C35-hop-17（21）-enes are identified by gas chromatography-mass spectrometry （GC-MS） analysis to exist as double isomers in most samples of the Aershan Formation and members 1 and 2 of the Tenggeer Formation from well SH3. Comprehensive organic geochemistry and organic petrology study indicates that algae and bacteria are the main biological source of lower Cretaceous sediments in the Saihantala Sag, and this is in accordance with the existence of hop-17（21）-enes. The similar distributions of hop-17（21）-enes and hopanes of these samples indicate that hop-17（21）-enes were transformed into hopanes through hydrogenation during diagenesis processes. The existence of hop-17（21）-enes means that not only the formation of organic matter is related to an anoxic environment and a biological source of algae and bacteria, but also hop-17（21）-enes are direct indicators of hydrocarbon rock at an immature to low-maturity stage. High hydrocarbon conversion ratio, algae and bacteria source and a high abundance of organic matter suggest that the Saihantala Sag has the potential to generate immature to low-maturity oil, which may be of great significance for oil exploration in the Erlian Basin.

Identification of a novel multifunctional oxidosqualene cyclase from Zea mays sheds light on the biosynthetic pathway of three pentacyclic triterpenoids

Zea mays(maize)is an important agricultural crop that produces a variety of valuable terpenoids,including several triterpenoids.However,no oxidosqualene cyclase(OSC)enzymes,which catalyze the first step in triterpenoid biosynthesis,have been identified in maize.Here,we identified a novel OSC(ZmOSC1)in maize using a combination of genomic mining and phylogenetic analyses.To functionally characterize the candidate OSC,we constructed a yeast strain that produced high levels of 2,3-oxidosqualene.When ZmOSC1 was expressed in this strain,three compounds were detected and identified as hop-17(21)-en-3-ol,hopenol B and simiarenol,respectively.For their biosynthesis,we proposed a potential cyclization mechanism catalyzed by ZmOSC1 via the generation of a dammarenyl cation,followed by sequential cationic ring expansion,cyclization,cationic migration and further proton elimination.This study discovered and characterized an OSC from maize for the first time,and laid a foundation to produce three bioactive pentacyclic triterpenes,hop-17(21)-en-3-ol,hopenol B and simiarenol,using synthetic biology approaches.