MSA - Systematics/Evolution
Hallen-Adams, Heather E , Luo, Hong , Walton, Jonathan .
Amanitins, phalloidins and prolyl-oligopeptidases: POP goes the toxin.
The lethal octapeptide amatoxins, and heptapeptide phallotoxins, of Amanita, Galerina, Lepiota and Conocybe are synthesized on ribosomes as 35 or 34-amino acid proproteins. The toxin proproteins have conserved Pro residues, one within the mature toxins and one flanking at the N-terminus. Based on this, we hypothesized that a Pro-specific peptidase catalyzes the initial processing of the proproteins. We have purified the processing peptidase from the phallotoxin-producing mushroom Conocbye albipes, cloned the gene, and shown that it is a prolyl oligopeptidase (POP) (EC 188.8.131.52). The POP enzyme of C. albipes cleaves a phalloidin precursor efficiently in a nonprocessive manner (indicated by transient accumulation of the N-terminal intermediate), but does not cleave an amanitin precursor efficiently.
Prolyl-oligopeptidases (POPs) cleave small peptides following proline residues. POPs are common in much of eukaryotic life, including animals, plants and basidiomycete fungi; oddly, genes with homology to POP genes appear to be lacking in the Ascomycota. Toxin producing species of Amanita (section Phalloideae) have two POP genes, one of which is present only in toxin producing species and one of which is found throughout the genus (based on Southern blot analyses). This suggests that the Amanita toxins might be processed by a special, dedicated POP distinct from the housekeeping POP. Galerina marginata, which makes amatoxins, also has two POP genes, but other basidiomycetes have only one.
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1 - Michigan State University, Department of Plant Biology & DOE Plant Research Laboratory, 166 Plant Biology Laboratories, East Lansing, MI, 48824-1312, USA
2 - Michigan State University, DOE Plant Research Laboratory, 106 Plant Biology Laboratories, East Lansing, MI, 48824-1312, USA
3 - Michigan State University, DOE Plant Research Laboratory & Department of Plant Biology, 106 Plant Biology Laboratories, East Lansing, MI, 48824-1312, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Cottonwood A/Snowbird Center
Date: Tuesday, July 28th, 2009
Time: 4:45 PM