The insect cytokine GBP was first isolated from Lepidoptera Mythimna (Pseudaletia) separata. It exerts multiple functions such as larval growth regulation, paralysis induction, plasmatocyte spreading induction, antimicrobial peptide expression, cell proliferation, embryogenesis, and cardioacceleration.
The M. separata proGBP consists of 152 aa with a bioactive mature GBP at the C-terminus. M. separata GBP consists of 23 aa with an intramolecular ring structure of 13 aa flanked by two Cys residues and with N-terminal and C-terminal extensions.NMR analysis showed that GBP consists of disordered N and C termini and a well-defined core stabilized by a disulfide bridge between two Cys residues, hydrophobic interactions, and a short β-hairpin.
Growth blocking peptide(GBP):MW 2494. pI 8.14 (M. separata GBP). Freely soluble in water and ethanol.
The fat body expresses 50 -terminal truncated forms of GBP transcript while the brain produces the 50 -terminal elongated form in M. separata larvae. The brain GBP gene consists of two exons separated by a single intron, which contains a GATA motif (TGATAA) and two cognates (KGATAW) that have been reported to be important for expression in the insect fat body.
The presence of GBP in the hemolymph of M. separata larvae parasitized by the parasitoid wasp Cotesia kariyai was reported in 1990, and was isolated and sequenced in 1991.
After the first report on M. separataGBP in 1990, various orthologs have been identified as peptides with different functions, as described above in Lepidoptera. GBP and other orthologs have been recognized as multifunctional cytokines since it was demonstrated in 2000 that both GBP and the plasmatocyte spreading peptide (PSP) induce larval growth retardation, plasmatocyte spreading, and larval paralysis.GBP secreted from the suboesophageal body plays an essential role in the formation of the procephalic domain during early embryogenesis.Furthermore, GBP enhances dopa decarboxylase (DDC) expression in the integuments, nervous tissues, and hemocytes of M. separata larvae, which elevates the dopamine concentrations in the hemolymph and nervous tissues. The GBPdopamine system has been proposed to regulate the induction of insect diapause as well as larval growth.GBP secreted from the suboesophageal body plays an essential role in the formation of the procephalic domain during early embryogenesis.When Drosophila GBP (CG15917) was first identified, four other homologous Drosophila genes were also found: CG11395, CG12517, CG14069, and CG17244. It has been recently found that GBP2 (CG11395) as well as GBP1 (CG15917) regulate the release of insulin-like peptides from the brain.
