Serine protease MP2 activates prophenoloxidase in the melanization immune response of Drosophila melanogaster

PLoS One. 2013 Nov 15;8(11):e79533. doi: 10.1371/journal.pone.0079533. eCollection 2013.

Abstract

In arthropods, melanization plays a major role in the innate immune response to encapsulate and kill the invasive organisms. It is mediated by a serine protease cascade and is regulated by serpins. The identification of the molecular components of melanization and the regulation of those components are still unclear in Drosophila melanogaster, although some genetic research on the activation of melanization has been reported. Here we report that Drosophila serine protease MP2 directly cleaves both recombinant and native prophenoloxidase-1. Overexpression or repression of MP2 in flies resulted in increased and decreased rates of cleavage, respectively, of prophenoloxidase-1. Moreover, serine protease inhibitor Spn27A formed SDS-stable complexes with MP2, both in vitro and in vivo. The amidase activity of MP2 was inhibited efficiently by Spn27A. Spn27A also prevented MP2 from cleaving prophenoloxidase-1. Taken together, these results indicate that under our experimental conditions MP2 functions as a prophenoloxidase-activating protease, and that this function is inhibited by Spn27A. MP2 and Spn27A thus constitute a regulatory unit in the prophenoloxidase activation cascade in Drosophila. The combination of genetic, molecular genetic and biochemical approaches should allow further advances in our understanding of the prophenoloxidase-activating cascade in insects and indirectly shed further light on protease-cascades in humans and other vertebrates.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Catechol Oxidase / genetics
  • Catechol Oxidase / metabolism*
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Drosophila melanogaster / enzymology*
  • Enzyme Precursors / genetics
  • Enzyme Precursors / metabolism*
  • Serine Proteases / genetics
  • Serine Proteases / metabolism*

Substances

  • Drosophila Proteins
  • Enzyme Precursors
  • pro-phenoloxidase
  • Catechol Oxidase
  • Serine Proteases

Grants and funding

This research was supported by National Natural Science Foundation of China (31172090), Program for New Century Excellent Talents in University (NCET-11-0476), and the 973 Program (2013CB114102). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.