Characterization of three neurosecretory proteins from the median neurosecretory cells of Locusta migratoria by coupled chromatographic, electrophoretic and isoelectrofocusing methods

Expression of neuroparsin cDNA in insect cells using baculovirus vectors

The cDNA encoding neuroparsin A, a polytropic neurohormone of the locust, Locusta migratoria, was inserted into the genome of Autographa californica nuclear polyhedrosis virus such that transcription was under control of the p10 promoter. A polypeptide having the same charge and the same apparent molecular weight as the authentic neuroparsin A and that was reactive against neuroparsin immune serum was produced in recombinant virus-infected lepidopteran cell lines but not in control virus-infected cells. The baculovirus-expressed polypeptide was purified by two steps of liquid chromatography (anion exchange and reversed phase) which were previously used to purify the natural neuroparsin. The purified baculovirus-expressed polypeptide enhanced fluid reabsorption of everted rectum preparations, as did the natural neuroparsin. Thus, this gene expression system produced a polypeptide identical to authentic neuroparsin.

Amino acid sequence of locust neuroparsins

Neuroparsins A and B were isolated from the nervous part of the corpus cardiaca of Locusta migratoria via a two-step purification procedure. Both consist of two polypeptide chains linked by disulfide bridges. The N-terminal sequence of both native neuroparsins was determined: the N-terminal end of neuroparsin B was unique while that of neuroparsin A showed three different sequences. These sequences were that of neuroparsin B and two others having five and two extra N-terminal residues. Neuroparsin B was found as a homodimer and the complete sequence of the monomer, determined from peptide fragments generated by treatment with cyanogen bromide and endoprotease Glu-C, comprises 78 residues.

Production and characterization of antibodies to neuroparsins A and B isolated from the corpora cardiaca of the locust

Antisera were raised in rabbits against neuroparsins A and B which were purified to near homogeneity using electroelution from 7.5% polyacrylamide electrophoresis gels. They were characterized using immunohistochemical, enzyme-linked immunosorbent assay (ELISA), and protein-blotting methods. The antineuroparsin A and the antineuroparsin B sera have different titers and sensitivities (higher titer for antineuroparsin A, higher sensitivity for antineuroparsin B). They exhibit very good specificity. The immunohistochemical study of the entire central nervous system using either antineuroparsin A or antineuroparsin B sera shows that only the A1 type of the protocerebral median neurosecretory cells are immunostained. Moreover, among the numerous proteins of the median region of the brain and of the corpora cardiaca, each immune serum recognized only neuroparsin A or neuroparsin B. Displacement curves obtained for each immune serum by competition between either neuroparsin A or neuroparsin B demonstrate that the neuroparsin A is recognized as well as neuroparsin B, with both antisera supporting the concept that these two proteins are chemically related. The nonspecific binding of neuroparsins to an antisomatostatin immune serum used at 1/100 dilution indicates that any cross-reactivities of invertebrate molecules obtained with very low dilutions of antisera to vertebrate molecules must be considered carefully before concluding any immunological relation between invertebrate and vertebrate products.