Immune challenge induces N-terminal cleavage of the Drosophila serpin Necrotic

• Published in: Insect biochemistry and molecular biology Vol. 36; no. 1; pp. 37 - 46
• Main Authors: Pelte, Nadège, Robertson, Andrew S., Zou, Zhen, Belorgey, Didier, Dafforn, Timothy R., Jiang, Haobo, Lomas, David, Reichhart, Jean-Marc, Gubb, David
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.01.2006; Elsevier
• Subjects: amino acid sequences; Animals; biochemical pathways; Biochemistry, Molecular Biology; Cellular Biology; Drosophila; Drosophila melanogaster - immunology; Drosophila melanogaster - metabolism; Drosophila Proteins - genetics; Drosophila Proteins - immunology; Drosophila Proteins - metabolism; enzyme cleavage; enzyme inhibition; Gene Expression Regulation; glutamine; Hemolymph proteins; immune response; Insect immunity; Life Sciences; Molecular biology; mutants; N-terminal amino acid sequences; Polyglutamine extension; Protein Conformation; proteinase inhibition; Proteinase inhibitor; proteinase inhibitors; serine proteinase inhibitors; serine proteinases; Serpins - genetics; Serpins - immunology; Serpins - metabolism; Signal Transduction; Toll pathway; Dif; CD; Toll pathway; Polyglutamine extension; Psh; PPE; Proteinase inhibitor; TUG; Nec-ΔN; Nec; PGRP; Nec-fl; Hemolymph proteins; GNBP; SI; Insect immunity; Ha; RCL; TLR; Spz; SP; HNE
• ISSN: 0965-1748; 1879-0240
• DOI: 10.1016/j.ibmb.2005.10.004

The Drosophila Necrotic protein is a serine proteinase inhibitor, which regulates the Toll-mediated innate immune response. Necrotic specifically inhibits an extracellular serine proteinase cascade leading to activation of the Toll ligand, Spätzle. Necrotic carries a polyglutamine extension amino-terminal to the core serpin structure. We show here that cleavage of this N-terminal extension occurs following immune challenge. This modification is blocked in PGRP-SA semmelweiss mutants after Gram-positive bacterial challenge and in persephone mutants after fungal or Gram-positive bacterial challenge, indicating that activation of either of the Toll pathway upstream branches induces N-terminal cleavage of the serpin. The absolute requirement of persephone gene product for this cleavage indicates that Gram-positive bacteria activate a redundant set of proteinases upstream of Toll. Both full-length Necrotic and the core serpin are active inhibitors of a range of serine proteinases: the highest affinity being for cathepsin G and elastases. We found a 13-fold increase in the specificity of the core serpin over that of full-length Necrotic for one of the tested proteinases (porcine pancreatic elastase). This finding indicates that cleavage of the Necrotic amino-terminal extension might modulate Toll activation following the initial immune response.