The antimicrobial properties of the puroindolines, a review

Authors: Morris, Craig

Submitted to: World Journal of Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2019
Publication Date: 5/28/2019
Citation: Morris, C.F. 2019. The antimicrobial properties of the puroindolines, a review. World Journal of Microbiology and Biotechnology. 35:86. https://doi.org/10.1007/s11274-019-2655-4.
DOI: https://doi.org/10.1007/s11274-019-2655-4

Interpretive Summary: Plants and animals are in a constant battle against pathogenic microbes. Human intervention in this struggle has relied heavily on synthetic compounds such as antibiotics and fungicides. However, the ability of microbes to develop resistance to these compounds necessitates alternative strategies. One such strategy is the use of antimicrobial proteins/peptides (AMPs). AMPs are small proteins and peptides, typically of <100 amino acid residues. Most are amphipathic and cationic; many specifically target features of the microbial cell membrane that are different from multicellular plants and animals. Puroindolines were first reported in 1990, and their discovery brought together two divergent fields of study. The first involved the genetic basis of wheat (Triricum ssp.) kernel texture (grain hardness). Kernel texture is fundamentally the single most important trait governing the milling, flour quality and food applications of wheat. The second field of study involved amphiphilic lipid binding proteins that were associated with the baking quality of wheat flour. A key aspect of this research was the isolation of proteins from wheat flour using Triton X-114, which can undergo a temperature dependent phase transition, producing ‘detergent rich’ and ‘detergent depleted’ fractions.

Technical Abstract: Antimicrobial peptides (AMPs) hold great promise in the control of animal and plant diseases with low risk of pathogen resistance. The two puroindolines, a and b, from wheat control endosperm softness of the wheat caryopsis (grain), but have also been shown to inhibit the growth and kill various bacteria and fungi, while showing little toxicity to erythrocytes. Puroindolines are small (~13 kDa) amphipathic proteins with a characteristic tryptophan-rich domain (TRD) that is part of 18 or 19 amino acid residue loop subtended by a disulfide bond. The present review presents a brief history of the puroindolines, their physical-chemical characteristics, their interaction with lipids and membranes, and their activity as AMPs. In this latter context, the use of the TRDs of puroindoline a and b in puroindoline AMP function is reviewed. The AMP activity of puroindoline a and b appear to act through similar but somewhat different modes, which may involve membrane binding, membrane disruption and ion channel formation, and intra-cellular nucleic acid binding and metabolic disruption. Natural and synthetic mutants have identified key elements of the puroindolines for antimicrobial activity.