Chemistry Reference
In-Depth Information
A highly homologous PKS-NRPS gene has been shown to be involved
in the biosynthesis of equisetin (
54
)in
Fusarium heterosporum
(20). EQS
posseses the same catalytic domains as FUSS, but examination of the structure
of (
54
) indicates that the pyrollidinone carbon derived from the carboxylate
of the amino acid (serine in this case) is not reduced, which indicates either
a reoxidation mechanism, or the fact that the R domain does not produce an
aldehyde intermediate in this case.
6.7 CONCLUSION
Recognition that the fungal PKS can be categorized into three subsets has allowed
more detailed consideration of the programming elements. The NR PKSs are
arranged into loading, extension, and processing components, and to some extent
this hypothesis has been verified by expression and study of individual catalytic
domains and by the construction of hybrid NR PKS genes. However, the program-
ming elements of the PR and HR PKS remain obscure. The first experiments to
probe programming in HR PKS have involved domain swaps, but few conclusions
have yet been drawn. Little information is known about the three-dimensional
structure of fungal PKS—whereas sequence and domain organization similarity
with mammalian FAS mean that broad descriptions of the architecture of the
catalytic domains can be modeled, detailed hypotheses that involve individual
domains or peptide motifs cannot yet be linked with programming.
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