title: Structural basis of the resistance of an insect carboxypeptidase to plant protease inhibitors.
abstract: Corn earworm (Helicoverpa zea), also called tomato fruitworm, is a common pest of many Solanaceous plants. This insect is known to adapt to the ingestion of plant serine protease inhibitors by using digestive proteases that are insensitive to inhibition. We have now identified a B-type carboxypeptidase of H. zea (CPBHz) insensitive to potato carboxypeptidase inhibitor (PCI) in corn earworm. To elucidate the structural features leading to the adaptation of the insect enzyme, the crystal structure of the recombinant CPBHz protein was determined by x-ray diffraction. CPBHz is a member of the A/B subfamily of metallocarboxypeptidases, which displays the characteristic metallocarboxypeptidase alpha/beta-hydrolase fold, and does not differ essentially from the previously described Helicoverpa armigera CPA, which is very sensitive to PCI. The data provide structural insight into several functional properties of CPBHz. The high selectivity shown by CPBHz for C-terminal lysine residues is due to residue changes in the S1' substrate specificity pocket that render it unable to accommodate the side chain of an arginine. The insensitivity of CPBHz to plant inhibitors is explained by the exceptional positioning of two of the main regions that stabilize other carboxypeptidase-PCI complexes, the beta8-alpha9 loop, and alpha7 together with the alpha7-alpha8 loop. The rearrangement of these two regions leads to a displacement of the active-site entrance that impairs the proper interaction with PCI. This report explains a crystal structure of an insect protease and its adaptation to defensive plant protease inhibitors.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Facultat de Ciències, and Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Spain.
authors.forename: Alex
authors.initials: A
authors.lastname: Bayés
authors.forename: Mireia
authors.initials: M
authors.lastname: Comellas-Bigler
authors.forename: Monica
authors.initials: M
authors.lastname: Rodríguez de la Vega
authors.forename: Klaus
authors.initials: K
authors.lastname: Maskos
authors.forename: Wolfram
authors.initials: W
authors.lastname: Bode
authors.forename: Francesc X
authors.initials: FX
authors.lastname: Aviles
authors.forename: Maarten A
authors.initials: MA
authors.lastname: Jongsma
authors.forename: Jules
authors.initials: J
authors.lastname: Beekwilder
authors.forename: Josep
authors.initials: J
authors.lastname: Vendrell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002268:Carboxypeptidases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D003460:Crystallization; D007313:Insecta / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010944:Plants / Q000737:chemistry*; D011480:Protease Inhibitors / Q000494:pharmacology*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D011480:Protease Inhibitors; D011994:Recombinant Proteins; D002268:Carboxypeptidases