The Family of MSDIN Cyclic Peptide Genes in Amanita phalloides and Amanita bisporigera

α-Amanitin and phallacidin are two bicyclic peptide toxins from the deadly Amanita genus of mushrooms.  These bicyclic peptides have unique structures and potent bioactivities, and these proteins are members of the MSDIN family, so named because of their first five conserved amino acids.  Proteins from MSDIN genes all have a conserved 10-amino acid C-terminal peptide sequence, a middle variable region of 6-10 amino acids and a conserved 17-amino acid N-terminal peptide sequence.  The amino acids of the variable region are processed into mature toxins by proteolytic excision, cyclization, cross-bridge formation, and hydroxylations.  The initial processing and cyclization reactions are performed by a specialized prolyl oligopeptidase called POPB.  We have generated draft genomes of two toxic fungi, A. bisporigera and A. phalloides, that both contain α-amanitin and phallacidin.  In addition to the genes for α-amanitin and phallacidin, these genomes contain many additional related sequences from the MSDIN gene family.  Based on the draft genomes, A. bisporigera has 36 MSDIN genes, and A. phalloides has 29.  However, only three genes are common to both genomes (α-amanitin, phallacidin, and one unnamed gene).  In A. bisporigera, transcript evidence indicates that 16 MSDIN family members are expressed.  The MSDIN gene family appears to have expanded rapidly and divergently since it arose within the genus Amanita.  Both A. bisporigera and A. phalloides are predicted to make an abundance of cyclic hexa-, hepta-, octa-, nona- and decapeptides, most of which have unknown biological activities.