Molecular requirements for the insecticidal activity of the plant peptide pea albumin 1 subunit b (PA1b).
PA1b (pea albumin 1, subunit b) is a small and compact 37-amino acid protein, isolated from pea seeds (Pisum sativum), that adopts a cystine knot fold. It acts as a potent insecticidal agent against major pests in stored crops and vegetables, making it a promising bioinsecticide. Here, we investigate the influence of individual residues on the structure and bioactivity of PA1b. A collection of 13 PA1b mutants was successfully chemically synthesized in which the residues involved in the definition of PA1b amphiphilic and electrostatic characteristics were individually replaced with an alanine. The three-dimensional structure of PA1b was outstandingly tolerant of modifications. Remarkably, receptor binding and insecticidal activities were both dependent on common well defined clusters of residues located on one single face of the toxin, with Phe-10, Arg-21, Ile-23, and Leu-27 being key residues of the binding interaction. The inactivity of the mutants is clearly due to a change in the nature of the side chain rather than to a side effect, such as misfolding or degradation of the peptide, in the insect digestive tract. We have shown that a hydrophobic patch is the putative site of the interaction of PA1b with its binding site. Overall, the mutagenesis data provide major insights into the functional elements responsible for PA1b entomotoxic properties and give some clues toward a better understanding of the PA1b mode of action.
Da Silva
Pedro
P
From the Institut National de la Recherche Agronomique (INRA), Institut National des Sciences Appliquées de Lyon (INSA-Lyon), IFR-41, UMR203 BF2I, Biologie Fonctionnelle, Insectes et Interactions, Université de Lyon, Bâtiment Louis Pasteur, F-69621 Villeurbanne. Electronic address: pedro.da-silva@insa-lyon.fr.
Rahioui
Isabelle
I
From the Institut National de la Recherche Agronomique (INRA), Institut National des Sciences Appliquées de Lyon (INSA-Lyon), IFR-41, UMR203 BF2I, Biologie Fonctionnelle, Insectes et Interactions, Université de Lyon, Bâtiment Louis Pasteur, F-69621 Villeurbanne.
Laugier
Christian
C
From the Institut National de la Recherche Agronomique (INRA), Institut National des Sciences Appliquées de Lyon (INSA-Lyon), IFR-41, UMR203 BF2I, Biologie Fonctionnelle, Insectes et Interactions, Université de Lyon, Bâtiment Louis Pasteur, F-69621 Villeurbanne.
Jouvensal
Laurence
L
Centre de Biophysique Moléculaire, UPR 4301 CNRS, University of Orléans and INSERM, rue Charles Sadron, 45071 Orléans Cedex 2.
Meudal
Hervé
H
Centre de Biophysique Moléculaire, UPR 4301 CNRS, University of Orléans and INSERM, rue Charles Sadron, 45071 Orléans Cedex 2.
Chouabe
Christophe
C
CNRS UMR 5123, Physiologie des Régulations Energétiques, Cellulaires et Moléculaires, Campus de la Doua, Université de Lyon 1, 69622 Villeurbanne, France.
Delmas
Agnès F
AF
Centre de Biophysique Moléculaire, UPR 4301 CNRS, University of Orléans and INSERM, rue Charles Sadron, 45071 Orléans Cedex 2.
Gressent
Frédéric
F
From the Institut National de la Recherche Agronomique (INRA), Institut National des Sciences Appliquées de Lyon (INSA-Lyon), IFR-41, UMR203 BF2I, Biologie Fonctionnelle, Insectes et Interactions, Université de Lyon, Bâtiment Louis Pasteur, F-69621 Villeurbanne.
D055516:2S Albumins, Plant / Q000737:chemistry*; D018360:Crystallography, X-Ray; D007306:Insecticides / Q000737:chemistry*; D009154:Mutation; D018532:Pisum sativum / Q000737:chemistry*; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D014118:Toxins, Biological / Q000737:chemistry*
D055516:2S Albumins, Plant; D007306:Insecticides; D021122:Protein Subunits; D014118:Toxins, Biological