Cofactors

There are no Cofactors for this Enzyme

Reaction Mechanism

ditrans,polycis-undecaprenyl-diphosphate synthase [(2E,6E)-farnesyl-diphosphate specific] By Reference

Undecaprenyl diphosphate synthases catalyse the sequential condensation of isopentyl diphosphate (IPP) with allylic disphosphates. The reaction generates linear prenyl diphosphates within the biosynthetic pathway of isoprenoid compounds; components which are essential to cell machinery such as cholesterol, carotenoids and dolichols. This reactions proceed through very similar mechanisms, although the enzymes differ with respect to the stereochemistry and chain length of their products. The enzyme in question is an example of the cis subclass.




The Mg dependent reaction begins with the elimination of a diphosphate ion from an allylic diphosphate to form an allylic cation at the C1 position. This cation is then attacked by the pi electrons at the C4' of the IPP with the formation of a new C-C bond between C1 and C4'. Several residues are involved in orientating the substrate molecule the direction necessary for stereospecific condensation with IPP to occur. It is still undecided whether the reaction proceeds via an ionization condensation elimination mechanism, where the carbocation is formed first, or by a concerted SN2 like mechanism where the abstraction of a proton from the C2 of IPP initiates the reaction. The residues implicated in an SN2 mechanism have been included in this annotation, although information on the alternative pathway can be found in the appended references. The crystal structure does not include the Mg metal or residues 74 to 85, and so Asn77, acting as a general base to IPP and Trp78, which orientates the diphosphate towards stereospecific condensation with IPP cannot be included in the annotation. The metal enhances the reactivity of the farnesyl pyrophosphate by polarising the O1-C'1 bond. The metal also acts to stabilise the resulting anion.

Catalytic Residues

AA	Uniprot	Uniprot Resid	PDB	PDB Resid
Leu	O82827	140	1f75	140
Asp	O82827	29	1f75	29
His	O82827	46	1f75	46
View Reaction Mechanisms in M-CSA

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Citations

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