Identification and characterization of Furins in larvae of Protaetia brevitarsis seulensis (Kolbe) (Coleoptera: Cetoniidae)

Furins are a family of proteases involved in the processing of many proproteins including growth regulators, immune proteins, and toxins. However, very few studies have been conducted on furin-like PCs in insects. Herein, we isolated and characterized full-length furin-like cDNAs (Psfurin-1 and Psfurin-2) from larvae of Protaetia brevitarsis seulensis (Kolbe). To search for furin-like PC cDNAs, we used high-throughput RNA sequencing (RNA-seq) expression profiling of data. The Psfurin-1 and Psfurin-2 transcripts, 2,370 and 3,702 nucleotides in length, respectively, encode peptides of 790 and 1,234 amino acids with calculated molecular masses of 88.3 and 135.6 kDa. We identified a consensus site for proprotein convertase that includes Asp, His, Asn, and Ser catalytic residues, and revealed the presence of a subtilisin-like serine protease/putative cell envelope proteinase domain related to the immune system. The predicted structures of the two proteins are very similar, but the cell envelope protease/immune-related domain differs somewhat. To examine the possible immune-related expression of Psfurin-1 and 2 transcripts, late larvae were injected with the Gram-negative bacterium Escherichia coli or the yeast Saccharomyces cerevisiae. Expression of Psfurin-1 mRNA in E. coli K12-challenged larvae was ~15-fold higher at 8 h and ~20-fold higher at 12 h than in LB medium-challenged control larvae. In the case of yeast-challenged larvae, expression of Psfurin-1 mRNA was not as elevated as in E. coli K12-challenged larvae, but expression was 4–5-fold higher than in LB medium-challenged larvae. Expression of Psfurin-2 mRNA in E. coli K12-challenged and yeast-challenged larvae was also significantly higher than in LB medium-challenged controls from 4 to 48 h, but expression levels were lower than for Psfurin-1 mRNA in both E. coli K12- and yeast-challenged larvae.