Pjk. Knight et al., MOLECULAR-CLONING OF AN INSECT AMINOPEPTIDASE-N THAT SERVES AS A RECEPTOR FOR BACILLUS-THURINGIENSIS CRYIA(C) TOXIN, The Journal of biological chemistry, 270(30), 1995, pp. 17765-17770
The Bacillus thuringiensis CryIA(c) insecticidal delta-endotoxin binds
to a 120 kDa glycoprotein receptor in the larval midgut epithelia of
the susceptible insect Manduca sexta. This glycoprotein has recently b
een purified and identified as aminopeptidase N. We now report the clo
ning of aminopeptidase N from a M. sexta midgut cDNA library. Two over
lapping clones were isolated, and their combined 3095-nucleotide seque
nce contains an open reading frame encoding a 990-residue prepro-prote
in. The N-terminal amino acid sequence derived from the glycoprotein i
s present in the open reading frame, immediately following a predicted
cleavable signal peptide and a pro-peptide. There are four potential
N-linked glycosylation sites. The C-terminal sequence contains a possi
ble glycosylphosphatidylinositol (GPI) anchor signal peptide, which su
ggests that, unlike most other characterized aminopeptidases, the lepi
dopteran enzyme is anchored in the membrane by a GPI anchor. This was
confirmed by partial release of aminopeptidase N activity from M. sext
a midgut brush border membranes by phosphatidylinositol-specific phosp
holipase C. The deduced amino acid sequence shows significant similari
ty to the zinc-dependent aminopeptidase gene family, particularly in t
he region surrounding the consensus zinc-binding motif characteristic
of these enzymes.