Isolation and structural determination of three peptides from the insect Locusta migratoria. Identification of a...

We have isolated three novel peptides from the aqueous extract of the pars intercerebralis of male and female adults of the insect Locusta migratoria. After extensive HPLC purification, the peptides were characterised by automated Edman degradation and electrospray mass spectrometry: one is a 35-residue peptide (3752.3 +/- 1.1 Da) containing six cysteines involved in three intramolecular disulfide bridges, the second is a 36-residue peptide (3919.2 +/- 0.9 Da), also cross-linked by three intramolecular disulfide bridges. This second peptide is post-translationally modified by a single fucose moiety, which was identified by gas chromatography coupled to mass spectrometry. These two peptides show a strong sequence similarity. Additionally, they were also found in larger amounts in the fat body of Locusta; this finding raises the question of their exact site of synthesis. The third peptide (5776.3 +/- 0.9 Da), a 54-residue peptide cross-linked by six intramolecular disulfide bridges, is structurally related to the two other peptides, but to a lesser extent. Mass spectrometry has shown that all the cysteines within these three peptides are involved in intramolecular disulfide bridges; however, the location of these bridges is not yet established and is currently being investigated. A computer search of sequence data banks did not reveal any significant similarity of these three peptides with other known proteins.