Identification, characterization and functional analysis of a serine protease inhibitor (Lvserpin) from the Pacific white shrimp, Litopenaeus vannamei

Abstract

As important arthropod immune responses, prophenoloxidase (proPO) activation and Toll pathway initiation are mediated by serine proteinase cascades and regulated by serpins. Herein, a serine protease inhibitor (Lvserpin), encoding for 415 amino acids with calculated molecular weight of 46,639Da and isoelectric point of 7.03 was characterized from the Pacific white shrimp Litopenaeus vannamei. Multiple sequence alignment revealed that Lvserpin shared the highest similarity with Penaeus monodon serpin6 (87%). Quantitative real-time PCR (qRT-PCR) results showed that the transcripts of Lvserpin were detected in all the examined tissues and most highly expressed in gill. The expression profiles of Lvserpin were greatly fluctuated upon infection of Vibrio anguillarum, Micrococcus lysoleikticus or White Spot Syndrome Virus (WSSV). Double stranded RNA-mediated suppression of Lvserpin resulted in a significant increase in the transcripts of two clip-domain serine proteinases (PPAE and PPAF), prophenoloxidase (proPO), anti-lipopolysaccharide factor (ALF), Crustin and penaeidin3 (Pens3) and also increased the high cumulative mortality post V. anguillarum injection. Besides, the recombinant Lvserpin protein (rLvserpin) was purified and exhibited inhibitory activity against trypsin. Also the rLvserpin showed inhibition on prophenoloxidase activation and bacterial growth. Hence, we proposed that the Lvserpin played important role in the shrimp innate immunity.