Research Highlight: rSp0032 has multitasking, anti-pathogen binding activities that predicts a flexible and effective immune response in sea urchins mediated by the Sp185/333 system

Abstract

The purple sea urchin, Strongylocentrotus purpuratus , possesses a sophisticated innate immune system that responds to microbes effectively by swift expression of the highly diverse Sp185/333 gene family. The encoded Sp185/333 proteins show significant sequence diversity and are predicted to have anti-pathogen functions. To address the anti-pathogen hypothesis, functional analysis of a recombinant Sp185/333 protein, rSp0032, shows that it exhibits specific binding to a marine Vibrio species and to Baker’s yeast but not to two Bacillus species. rSp0032 binds to lipopolysaccharide (LPS), β-1,3-glucan and flagellin but not to peptidoglycan. rSp0032 binding to LPS is competed by LPS, β-1,3-glucan and flagellin but not by peptidoglycan. In silico predictions suggest that rSp0032 is intrinsically disordered and its multiple binding targets suggest adoption of different conformations for binding to different PAMPs and pathogens. Based on rSp0032 binding to a range of targets, and that hundreds of different isoforms of Sp185/333 proteins are expressed in individual sea urchins, each may have different binding activities imparting a wide range of overlapping binding targets by this family of immune response proteins. The outcome may be very effective host protection against a broad array of potential pathogens in the marine environment.