SPP-3, a saposin-like protein of Caenorhabditis elegans, displays antimicrobial and pore-forming activity and is located in the intestine and in one head neuron

Caenopores belong to the saposin-like protein superfamily in Caenorhabditis elegans with 33 putative antimicrobial and pore-forming proteins. In this study, we analysed one selected member of this multifarious protein family, namely SPP-3, in detail, as its coding gene has been described to be inducible after bacterial challenge. The recombinant protein was antimicrobially active against a wide range of gram-negative and gram-positive bacteria and displayed membrane-permeabilizing and pH-dependent pore-forming activity. Promoter activity of the respective gene, spp-3, was localized to the intestine and the head neuron SDQR. While gene silencing had no apparent effect on the number of surviving Escherichia coli bacteria in the intestine, it increased the egg laying significantly. Accordingly, SPP-3 is a protein with antimicrobial activity that is presumably part of the redundant armamentarium of effector proteins in the worm’s intestine, may help to protect neurons, and appears to be involved in regulating reproduction.

► SPP-3 is antimicrobially active against a variety of bacterial strains. ► SPP-3 acts by permeabilizing the cytoplasmic membrane of bacteria. ► SPP-3 is a pore-forming protein and hence belongs to the caenopore family. ► The expression of spp-3 was localized to the intestine and the head neuron SDQR. ► Gene-silencing revealed an impact of spp-3 on the regulation of reproduction.