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

Abstract

A new family of antimicrobial peptides has been discovered in Macadamia integrifolia. The first member of this new family to be purified from nut kernels was a peptide of 45 aa residues, termed MiAMP2c. This peptide inhibited various plant pathogenic fungi in vitro. cDNA clones corresponding to MiAMP2c encoded a 666 aa precursor protein homologous to vicilin 7S globulin proteins. The deduced precursor protein sequence contained a putative hydrophobic N-terminal signal sequence (28 aa), an extremely hydrophilic N-proximal region (212 aa), and a C-terminal region of 426 aa which is represented in all vicilins. The hydrophilic portion of the deduced protein contained the 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 contained a C-X-X-X-C-(10-12)X-C-X-X-X-C motif. Subsequent isolations from seed exudates led to the purification of the predicted family members MiAMP2b and 2d, both of which also exhibited antimicrobial activity in vitro. These results suggest that some vicilins play a role in defence during seed germination.