Biomedical Engineering Reference
In-Depth Information
another fungus,
Acremonium chrysogenum
, or a genetically engineered
P.
chrysogenum
(reviewed in Gidijala et al. 2010).
The current production
P. chrysogenum
production strains have titers
well over 50 g/l penicillinG (Demain and Elander 1999) and are derived
from the early natural isolates by repetitive classical mutagenesis rounds
leading to various genome modifi cations. Four biosynthetical enzymes are
involved in converting the aminoacids aminoadipate, cysteine and valine in
to penicillin: δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS),
isopenicillinN synthase (IPNS), isopenicillinN:acyltransferase (AT) and,
depending on the side-chain, various acyl-CoA ligases.
These four enzymes can convert non-penicillin producing species as
baker's yeast in to penicillin producing species (Gidijala et al. 2009). The
genes encoding the fi rst three enzymes are clustered together and amplifi ed
in
Penicillium
production strains (Fierro et al. 1995). The enzymes and thus
penicillin synthesis, are highly controlled indirect via glucose repression
of the genes (Revilla et al. 1986), or direct via various types of inhibition
(Ramos et al. 1985, Perry et al. 1988, Theilgaard et al. 1997), high enzyme
turnover (Theilgaard et al. 1997) and intracellular compartmentalization
(Evers et al. 2004). Most of the control is at the fi rst two enzymes ACVS,
a very large non-ribosomal peptide synthetase catalyzing the tripeptide
formation and IPNS, catalyzing the oxygen-dependent formation of
the β-lactam ring structure and sensitive to a wide range of molecules
(glutathione, metal ions, CO
2
, bis-ACV). Several fungal genes were shown
to enhance the productivity (Theilgaard et al. 2001, Kiel et al. 2005, Lamas-
Maceiras et al. 2006).
Statins
From an economic point of the view, the cholesterol lowering class of
statins might even outcompete the β-lactams. With obesity becoming
a huge problem, blood cholesterol levels need to be controlled and the
most effective available drugs are statins. Compounds like atorvastatin
and simvastatin are the top-selling drugs in the US. And while the former
is a synthetic compound, simvastatin and the related pravastatin are
semi-synthetics derived from fungal secondary metabolites, respectively
lovastatin and compactin (see
Fig. 3
for the general structure). The fi rst
statin, compactin, was discovered in the early 70ies during a screening
program of the Japanese Sankyo Co. Ltd.
Like the β-lactam genes the biosynthetic statin genes are clustered
together (Hutchinson et al. 1999, Abe et al. 2002a) and highly regulated,
although by cluster specifi c transcription factors clustered together with
the biosynthetic genes (Abe et al. 2002b). Increasing the gene (cluster) copy
