Plant defensins: Common fold, multiple functions

Plant defensins represent a large class of structurally similar peptides found throughout the plant kingdom. Despite a conserved cysteine spacing pattern and three-dimensional structure, their sequences are highly divergent and they display a range of activities including antifungal and antibacterial activities, enzyme inhibitory activities as well as roles in heavy metal tolerance and development. The vast number of sequences along with their diverse range of activities makes it impossible to test the activity and assign function to all plant defensins. However, as the number of characterized defensins increases, in depth sequence analysis may allow us to predict the function of newly identified peptides. In this review, we analyze the sequences of defensins whose activities have been described and group these based on similarity using a maximum-likelihood phylogenetic tree. We also compare the amino acids that have been described as essential for the activity of various plant defensins between these groups. While many more plant defensins will need to be characterized before we can develop rules to predict the activity of novel sequences, this approach may prove useful in identifying structure-function relationships.