A quantitative peptidomics approach to unravel immunological functions of angiotensin converting enzyme in Locusta migratoria

• Locust orthologue of angiotensin converting enzyme (LmACE) is an extracellular protein encoded by multiple exons.
• Following LPS or PGN challenge, LmACE transcript was upregulated in hemocytes but not in fat body.
• Differential peptidomics of peptides in circulation unraveled putative enzymatic roles of LmACE.

Locusta migratoria angiotensin converting enzyme (LmACE) is encoded by multiple exons displaying variable number of genomic duplications. Treatments of lipopolysaccharide (LPS) as well as peptidoglycan but not β-1-3 glucan resulted in enhanced expression of angiotensin converting enzyme in hemocytes of Locusta migratoria. No such effect was observed in fat body cells. Differential peptidomics using locust plasma samples post infection with LPS in combination with both an LmACE transcript knockdown by RNAi and a functional knockdown using captopril allowed the identification of 5 circulating LPS induced peptides which only appear in the hemolymph of locust having full LmACE functionality. As these peptides originate from larger precursor proteins such as locust hemocyanin-like protein, having known antimicrobial properties, the obtained results suggest a possible direct or indirect role of LmACE in the release of these peptides from their precursors. Additionally, this experimental setup confirmed the role of LmACE in the clearance of multiple peptides from the hemolymph.