Identification and characterization of serpin genes in Manduca sexta

Abstract

Insects adopt a variety of immune mechanisms to defend against invading pathogens, such as phagocytosis, encapsulation, melanization and antimicrobial peptide synthesis. Serine protease cascades play an important role in some of these immune responses, and serpins (serine protease inhibitors) regulate the proteases after zymogen activation. Serpins are a superfamily of proteins, which share a conserved tertiary structure composed of three β‐sheets, 8–9 α‐helices, and an exposed reactive center loop (RCL). Once encountering its specific serpin, the protease cleaves the serpin RCL at the scissile bond, resulting in the insertion of RCL into β‐sheet A as a new strand and the formation of an irreversible inhibitory complex. Our group uses Manduca sexta a model insect to study the insect immune system. By searching the whole genome of M. sexta, 32 serpin genes were identified. MsSerpin1, 15 and 28 are capable of encoding more than one polypeptide with different RCL sequences via alternative splicing. Besides 12 isoforms of MsSerpin1 previously known, two additional isoforms were identified, increasing the total number of splicing isoforms of MsSerpin1 to 14. Phylogenetic analysis of serpins in M. sexta and the silk worm Bombyx mori indicate evolutionary conservation of some serpins, with 17 orthologous pairs identified. These include 7 characterized M. sexta serpins that are involved in protease cascades activating the prophenoloxidase or Toll immune pathways. The majority of M. sexta and B. mori serpin genes contain 6–10 exons except for a clade including 10 M. sexta serpin genes and 7 B. mori serpin genes with only 1–3 exons. The analysis of RCL regions indicates that about three quarters of M. sexta serpin proteins are likely to be inhibitory. Transcription level of MsSerpin‐1–7, 11–12, 14–15, 17–18 and 22 displayed an up‐regulation in fat body or hemocytes upon immune challenge. Transcript profiles give hints to the temporal and spatial expression patterns of each serpin, which lead to suggestions for their functional study in the future.Support or Funding InformationNIH grants GM041247, GM58634 and AI11266This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.