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Characterization of a digestive carboxypeptidase from the insect pest corn earworm (Helicoverpa armigera) with novel specificity towards C-terminal glutamate residues.

Bown, D. P. and Gatehouse, J. A. (2004) 'Characterization of a digestive carboxypeptidase from the insect pest corn earworm (Helicoverpa armigera) with novel specificity towards C-terminal glutamate residues.', European journal of biochemistry., 271 (10). pp. 2000-2011.


Carboxypeptidases were purified from guts of larvae of corn earworm (Helicoverpa armigera), a lepidopteran crop pest, by affinity chromatography on immobilized potato carboxypeptidase inhibitor, and characterized by N-terminal sequencing. A larval gut cDNA library was screened using probes based on these protein sequences. cDNA HaCA42 encoded a carboxypeptidase with sequence similarity to enzymes of clan MC [Barrett, A. J., Rawlings, N. D. & Woessner, J. F. (1998) Handbook of Proteolytic Enzymes. Academic Press, London.], but with a novel predicted specificity towards C-terminal acidic residues. This carboxypeptidase was expressed as a recombinant proprotein in the yeast Pichia pastoris. The expressed protein could be activated by treatment with bovine trypsin; degradation of bound pro-region, rather than cleavage of pro-region from mature protein, was the rate-limiting step in activation. Activated HaCA42 carboxypeptidase hydrolysed a synthetic substrate for glutamate carboxypeptidases (FAEE, C-terminal Glu), but did not hydrolyse substrates for carboxypeptidase A or B (FAPP or FAAK, C-terminal Phe or Lys) or methotrexate, cleaved by clan MH glutamate carboxypeptidases. The enzyme was highly specific for C-terminal glutamate in peptide substrates, with slow hydrolysis of C-terminal aspartate also observed. Glutamate carboxypeptidase activity was present in larval gut extract from H. armigera. The HaCA42 protein is the first glutamate-specific metallocarboxypeptidase from clan MC to be identified and characterized. The genome of Drosophila melanogaster contains genes encoding enzymes with similar sequences and predicted specificity, and a cDNA encoding a similar enzyme has been isolated from gut tissue in tsetse fly. We suggest that digestive carboxypeptidases with sequence similarity to the classical mammalian enzymes, but with specificity towards C-terminal glutamate, are widely distributed in insects.

Item Type:Article
Keywords:Clan MC metalloproteinase, digestive proteinase, glutamatecarboxypeptidase, Insect herbivore, Proteinase activation, Rat carboxypeptidase, Lacanobia-oleracea, Noctuidae larvae, Midgut cells, CDNA cloning, Gene family, Tomato moth, Procarboxypeptidase, Enzyme.
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Record Created:12 Feb 2009
Last Modified:08 Apr 2009 16:31

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