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Entry M0254    5.4.99.17    squalene-hopene cyclase

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Step 04

The initially formed 5-membered ring expands and the final 5-membered ring is formed in an intramolecular electrophilic addition.

GIF of Reaction Step M0254.stg04


Comment: The cyclization reaction is subsequently followed by D-ring expansion and Markovnikov E-ring closure, yielding the tertiary hopanyl C-22 cation with the 6.6.6.6.5-fused pentacyclic ring system, which is likely to be stabilized by the conserved Phe605 pi-electrons [1].



Mechanisms

Intramolecular Electrophilic Addition

Mechanism Components

Bond Formation
Bond Cleavage
Bond Order Change
Intermediate Formation
Cyclisation

Amino acids involved in the reaction step.

Amino Acid Location of Function Activity Function
Asp376 Side Chain spectator Hydrogen Bond Acceptor
His451 Side Chain spectator Hydrogen Bond Donor
Electrostatic Stabiliser
Tyr495 Side Chain spectator Hydrogen Bond Donor
Electrostatic Stabiliser
Phe365 Side Chain spectator van der Waals interaction
Tyr420 Side Chain spectator van der Waals interaction
Polar Non-polar interaction
Trp489 Side Chain spectator van der Waals interaction
Polar Non-polar interaction
Tyr609 Side Chain spectator van der Waals interaction
Polar Non-polar interaction
Phe601 Side Chain spectator van der Waals interaction
Phe605 Side Chain spectator van der Waals interaction
Electrostatic Stabiliser
Trp169 Side Chain spectator van der Waals interaction
Polar Non-polar interaction
Glu45 Side Chain spectator Hydrogen Bond Acceptor

Reactive Centre

Bonds Formed Bonds Cleaved Bonds Changed in Order Atom Types Involved
C-C
C-C
C-C
The C-C bond changes from a double to single bond
C

View similar reactions in MACiE.


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