Pyrrolnitrin

Biosynthesis

In Pseudomonas fluorescens, biosynthesis of pyrrolnitrin requires four genes, named prnABCD, arranged into a single operon*.* The products of these genes are similar in size and catalyze four subsequent reactions:

• prnA – chlorination of L-tryptophan to 7-chloro-L-tryptophan (7-CLT), in a process requiring NAD
• prnB – ring rearrangement and decarboxylation of 7-chloro-L-tryptophan to form monodechloroaminopyrrolnitrin (MAD)
• prnC – chlorination of monodechloroaminopyrrolnitrin to form aminopyrrolnitrin (APRN), in a process also requiring NAD
• prnD – oxidation of the amino group of APRN to a nitro group thus completing the biosynthesis of pyrrolnitrin.

Except for prnA, these enzymes are unable to act on D-tryptophan.

Neither of the chlorinating enzymes, prnA nor prnC, show homology to known haloperoxidases nor to one another.

An alternative pathway was also suggested, where L-tryptophan is first turned into aminophenylpyrrole (APP) and then by subsequent steps to aminopyrrolnitrin and pyrrolnitrin. While these steps have not been described in more detail, prnB is able to produce APP, presumably from tryptophan as starting material. APP seems to be an unwanted side product. The gene coding for prnB also starts with the unusual GTG start codon, further lowering the amount of prnB expressed and thus lowering the amount of present APP.

References

References

1. (April 1998). "Functions Encoded by Pyrrolnitrin Biosynthetic Genes from Pseudomonas fluorescens". Journal of Bacteriology.
2. (2007-10-01). "The Second Enzyme in Pyrrolnitrin Biosynthetic Pathway Is Related to the Heme-Dependent Dioxygenase Superfamily". Biochemistry.
3. (2003). "Encyclopedia of Agrochemicals".
4. (1993). "Biochemical Effects of the Phenylpyrrole Fungicide Fenpiclonil in Fusarium sulphureum (Schlecht)". Pesticide Biochemistry and Physiology.