Solution structure of the plant defensin VrD1 from mung bean and its possible role in insecticidal activity against bruchids.
Vigna radiata plant defensin 1 (VrD1) is the first reported plant defensin exhibiting insecticidal activity. We report herein the nuclear magnetic resonance solution structure of VrD1 and the implication on its insecticidal activity. The root-mean-square deviation values are 0.51 +/- 0.35 and 1.23 +/- 0.29 A for backbone and all heavy atoms, respectively. The VrD1 structure comprises a triple-stranded antiparallel beta-sheet, an alpha-helix, and a 3(10) helix stabilized by four disulfide bonds, forming a typical cysteine-stabilized alphabeta motif. Among plant defensins of known structure, VrD1 is the first to contain a 3(10) helix. Glu26 is highly conserved among defensins; VrD1 contains an arginine at this position, which may induce a shift in the orientation of Trp10, thereby promoting the formation of this 3(10) helix. Moreover, VrD1 inhibits Tenebrio molitor alpha-amylase. Alpha-amylase has an essential role in the digestion of plant starch in the insect gut, and expression of the common bean alpha-amylase inhibitor 1 in transgenic pea imparts complete resistance against bruchids. These results imply that VrD1 insecticidal activity has its basis in the inhibition of a polysaccharide hydrolase. Sequence and structural comparisons between two groups of plant defensins having different specificity toward insect alpha-amylase reveal that the loop between beta2 and beta3 is the probable binding site for the alpha-amylase. Computational docking experiments were used to study VrD1-alpha-amylase interactions, and these results provide information that may be used to improve the insecticidal activity of VrD1.
Department of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan.
Yaw-Jen
YJ
Liu
Chao-Sheng
CS
Cheng
Szu-Ming
SM
Lai
Ming-Pin
MP
Hsu
Ching-San
CS
Chen
Ping-Chiang
PC
Lyu
D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D023082:Defensins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D007887:Fabaceae / Q000737:chemistry* / Q000378:metabolism / Q000469:parasitology; D007306:Insecticides / Q000737:chemistry* / Q000494:pharmacology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010940:Plant Proteins / Q000737:chemistry* / Q000494:pharmacology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D013712:Tenebrio / Q000187:drug effects* / Q000201:enzymology; D000516:alpha-Amylases / Q000037:antagonists & inhibitors / Q000378:metabolism
D023082:Defensins; D007306:Insecticides; D010940:Plant Proteins; D000516:alpha-Amylases