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Saikia S, Parker EJ, Koulman A, Scott B. Biol Chem. 2007 Jun
8;282(23):16829-37.
Defining paxilline biosynthesis in Penicillium paxilli:
functional characterization of two cytochrome P450
monooxygenases.
Institute of Molecular Biosciences, Massey University,
Palmerston North, New Zealand.
Indole diterpenes are a large, structurally and functionally
diverse group of secondary metabolites produced by filamentous
fungi. Biosynthetic schemes have been proposed for these
metabolites but until recently none of the proposed steps had
been validated by biochemical or genetic studies. Using
Penicillium paxilli as a model experimental system to study
indole diterpene biosynthesis we previously showed by deletion
analysis that a cluster of seven genes is required for paxilline
biosynthesis. Two of these pax genes, paxP and paxQ (encoding
cytochrome P450 monooxygenases), are required in the later steps
in this pathway. Here, we describe the function of paxP and paxQ
gene products by feeding proposed paxilline intermediates to
strains lacking the pax cluster but containing ectopically
integrated copies of paxP or paxQ. Transformants containing paxP
converted paspaline into 13-desoxypaxilline as the major product
and beta-PC-M6 as the minor product. beta-PC-M6, but not
alpha-PC-M6, was also a substrate for PaxP and was converted to
13-desoxypaxilline. paxQ-containing transformants converted
13-desoxypaxilline into paxilline. These results confirm that
paspaline, beta-PC-M6, and 13-desoxypaxilline are paxilline
intermediates and that paspaline and beta-PC-M6 are substrates
for PaxP, and 13-desoxypaxilline is a substrate for PaxQ. PaxP
and PaxQ also utilized beta-paxitriol and alpha-PC-M6 as
substrates converting them to paxilline and alpha-paxitriol,
respectively. These findings have allowed us to delineate
clearly the biosynthetic pathway for paxilline for the first
time.
PMID: 17428785 |
