Isolation and structural characterization of an insulin‐related molecule, a predominant neuropeptide from Locusta migratoria

Neurohaemal lobes of corpora cardiaca of Locusta migratoria are an established storage site for neurohormones produced by the neurosecretory cells of the brain. As previously reported [Hietter, H., Van Dorsselaer, A., Green, B., Denoroy, L., Hoffmann, J. A. & Luu, B. (1990) Eur. J. Biochem. 187 , 241–247], the isolation and characterization of a novel 5‐kDA peptide from these lobes served as the basis for oligonucleotide screening of cDNA libraries prepared from poly(A)RNA from neurosecretory cells of the central nervous system. From subsequent cDNA cloning studies [Lagueux, M., Lwoff, L., Meister, M., Goltzené, F. & Hoffmann, J. A. (1991) Eur. J. Biochem. 187 , 249–254], the existence of a 145‐residue precursor protein was deduced, which contained, in addition to the 5‐kDa peptide, amino‐acid sequences with homology to the A and B chains of an insulinrelated peptide. In the present study we have isolated the native molecule from corpora cardiaca of Locusta and characterized, by Edman degradation and plasma‐desorption mass spectrometry, the two chains as follows: A chain, Gly‐Val‐Phe‐Asp‐Glu‐Cys‐Cys‐Arg‐Lys‐Ser‐Cys‐Ser‐Ile‐Ser‐Glu‐Leu‐Gln‐Thr‐Tyr‐Cys‐Gly (Ile, isoleucine); B chain, Ser‐Gly‐Ala‐Pro‐Gln‐Pro‐Val‐Ala‐Alg‐Tyr‐Cys‐Gly‐Glu‐Lys‐Leu‐Ser‐Asn‐Ala‐Leu‐Lys‐Leu‐Val‐Cys‐Arg‐Gly‐Asn‐Tyr‐Asn‐Thr‐Met‐Phe. Taken in conjunction with the previous cloning studies, our data lead to a clear picture of the processing of Locusta preproinsulin. They indicate that locusta corpora cardiaca contain remarkably large amounts of one single insulin form, in contrast to multiple insulin isoforms of Bombyx mori , the only other insect species from which insulin‐related peptides have been isolated and characterized [Nagasawa, H., Kataoka, H., Isogai, A., Tamura, S., Suzuki, A., Mizoguchi, A., Fujiwara, Y., Suzuki, A., Takahashi, S. & Ishizaki, H. (1986) Proc. Natl Acad. Sci. USA 83 , 5840–5843].