The Journal of Neuroscience, June 1, 1999, 19(11):4280-4292
Cloning and Characterization of Aplysia Neutral
Endopeptidase, a Metallo-Endopeptidase Involved in the Extracellular
Metabolism of Neuropeptides in Aplysia californica
Jacques P.
Zappulla1,
Louise
Wickham1,
Wafa
Bawab1,
Xiao-Feng
Yang1,
Maksim V.
Storozhuk2,
Vincent F.
Castellucci2, 3, and
Luc
DesGroseillers1, 3
1 Département de Biochimie,
2 Département de Physiologie, and
3 Centre de Recherches en Sciences Neurologiques,
Université de Montréal, Montréal, Québec,
Canada, H3C 3J7
Cell surface metallo-endopeptidases play important roles in cell
communication by controlling the levels of bioactive peptides around
peptide receptors. To understand the relative relevance of these
enzymes in the CNS, we characterized a metallo-endopeptidase in the CNS
of Aplysia californica, whose peptidergic pathways are
well described at the molecular, cellular, and physiological levels.
The membrane-bound activity cleaved Leu-enkephalin at the
Gly3-Phe4 bond with an inhibitor
profile similar to that of the mammalian neutral endopeptidase (NEP).
This functional homology was supported by the molecular cloning of
cDNAs from the CNS, which demonstrated that the Aplysia
and mammalian NEPs share all the same amino acids that are essential
for the enzymatic activity. The protein is recognized both by specific
anti-Aplysia NEP (apNEP) antibodies and by the
[125I]-labeled NEP-specific inhibitor RB104,
demonstrating that the apNEP gene codes for the
RB104-binding protein. In situ hybridization experiments
on sections of the ganglia of the CNS revealed that apNEP is expressed
in neurons and that the mRNA is present both in the cell bodies and in
neurites that travel along the neuropil and peripheral nerves. When
incubated in the presence of a specific NEP inhibitor, many neurons of
the buccal ganglion showed a greatly prolonged physiological response
to stimulation, suggesting that NEP-like metallo-endopeptidases may
play a critical role in the regulation of the feeding behavior in
Aplysia. One of the putative targets of apNEP in this
behavior is the small cardioactive peptide, as suggested by RP-HPLC
experiments. More generally, the presence of apNEP in the CNS and
periphery may indicate that it could play a major role in the
modulation of synaptic transmission in Aplysia and in
the metabolism of neuropeptides close to their point of release.
Key words:
Aplysia; neutral endopeptidase; CNS; neuropeptide degradation; buccal ganglion; SCP
Copyright © 1999 Society for Neuroscience 0270-6474/99/19114280-13$05.00/0