Structure and Activity of the Insect Cytokine Growth-blocking Peptide

• Published in: The Journal of biological chemistry Vol. 276; no. 34; pp. 31813 - 31818
• Main Authors: Aizawa, Tomoyasu, Hayakawa, Yoichi, Ohnishi, Atsushi, Fujitani, Naoki, Clark, Kevin D., Strand, Michael R., Miura, Kazunori, Koganesawa, Nozomi, Kumaki, Yasuhiro, Demura, Makoto, Nitta, Katsutoshi, Kawano, Keiichi
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 24.08.2001
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M105251200

Growth-blocking peptide (GBP) is a 25-amino acid insect cytokine found in Lepidopteran insects that possesses diverse biological activities such as larval growth regulation, cell proliferation, and stimulation of immune cells (plasmatocytes). The tertiary structure of GBP consists of a structured core that contains a disulfide bridge and a short antiparallel β-sheet (Tyr 11 –Arg 13 and Cys 19 –Pro 21 ) and flexible N and C termini (Glu 1 –Gly 6 and Phe 23 –Gln 25 ). In this study, deletion and point mutation analogs of GBP were synthesized to investigate the relationship between the structure of GBP and its mitogenic and plasmatocyte spreading activity. The results indicated that deletion of the N-terminal residue, Glu 1 , eliminated all plasmatocyte spreading activity but did not reduce mitogenic activity. In contrast, deletion of Phe 23 along with the remainder of the C terminus destroyed all mitogenic activity but only slightly reduced plasmatocyte spreading activity. Therefore, the minimal structure of GBP containing mitogenic activity is 2–23 GBP, whereas that with plasmatocyte spreading activity is 1–22 GBP. NMR analysis indicated that these N- and C-terminal deletion mutants retained a similar core structure to wild-type GBP. Replacement of Asp 16 with either a Glu, Leu, or Asn residue similarly did not alter the core structure of GBP. However, these mutants had no mitogenic activity, although they retained about 50% of their plasmatocyte spreading activity. We conclude that specific residues in the unstructured and structured domains of GBP differentially affect the biological activities of GBP, which suggests the possibility that multifunctional properties of this peptide may be mediated by different forms of a GBP receptor.