Poster: Enzymology

Abs # 258: Isoprenoid biosynthesis in maize: Is there more than one role for farnesyl pyrophosphate synthase?

Presenter:	Cervantes-Cervantes, Miguel , mcclc@cunyvm.cuny.edu
Authors	Cervantes-Cervantes, Miguel  (A)   Wurtzel, Eleanore T. (A) (B)
Affiliations:	(A): Department of Biological Sciences, Lehman College-City University of New York (CUNY) (B): Graduate School and University Center-CUNY
Web Site:	http://a32.lehman.cuny.edu/webcervantes/index.html

Isoprenoids constitute a large, structurally diverse family of compounds synthesized by both prokaryotes and eukaryotes. In plants, isoprenoids include the phytol chain of chlorophyll, the allylic moieties of farnesylated and geranylgeranylated proteins, and complex molecules such as taxenes, terpenes, rubber, gibberellins, and carotenoids. Isoprenyl pyrophosphate synthases catalyze the incorporation of isopentenyl pyrophosphate (IPP; C₅) units onto other allylic pyrophosphate substrates. These enzymes differ in the number of IPP units they incorporate and consequently the chain length of their products. Using a fucntional complementation approach in Escherichia coli, we cloned several maize (Zea mays) endosperm cDNAs capable of alleviating the crtE deletion of the Erwinia uredovora carotenogenic cluster, as indicated by the production of zeaxanthin, a yellow carotenoid. CRTE encodes the microbial version of geranylgeranyl pyrophosphate synthase (GGPPS). The predicted amino acid sequence of our cDNAs showed farnesyl pyrophosphate synthase (FPPS) signatures. Using extracts of E. coli transformed with one of the maize cDNAs, enzymatic assays were done with dimethylallyl pyrophostate and [¹⁴C]-IPP as substrates to confirm product specificity. Besides farnesyl pyrophosphate (C₁₅), geranylgeranyl pyrophosphate (C₂₀) was also produced. Other plant cDNAs encoding isoprenoid synthetases were tested to prove the apparent lack of specificity of this maize enzyme. Given the course of appearance of the mRNA for this isoprenoid synthase during maize endosperm development it is fitting to ask if there is more than one metabolic role for this seemingly bifunctional isoprenoid synthase.