A family of antimicrobial peptides is produced by processing of a 7S globulin protein in Macadamia integrifolia kernels

A new family of antimicrobial peptides has been discovered in Macadamia int egrifolia. The first member of this new family to be purified from nut kern els was a peptide of 45 aa residues, termed MiAMP2c. This peptide inhibited various plant pathogenic fungi in vitro. cDNA clones corresponding to MiAM P2c encoded a 666 aa precursor protein homologous to vicilin 7S globulin pr oteins. The deduced precursor protein sequence contained a putative hydroph obic N-terminal signal sequence (28 aa), an extremely hydrophilic N-proxima l region (212 aa), and a C-terminal region of 426 aa which is represented i n all vicilins. The hydrophilic portion of the deduced protein contained th e sequence for MiAMP2c as well as three additional segments having the same cysteine spacing pattern as MiAMP2c. Each member of the MiAMP2 family (i.e . MiAMP2a, b, c and d) consisted of approximately 50 amino acids and contai ned a C-X-X-X-C-(10-12)X-C-X-X-X-C motif. Subsequent isolations from seed e xudates led to the purification of the predicted family members MiAMP2b and 2d, both of which also exhibited antimicrobial activity in vitro. These re sults suggest that some vicilins play a role in defence during seed germina tion.