Caenopore-5: the three-dimensional structure of an antimicrobial protein from Caenorhabditis elegans

The caenopore-5 protein encoded by the spp-5 gene is one of the 33 caenopores identified in Caenorhabditis elegans and is a pore-forming peptide which plays an important role in the elimination of Escherichia coli ingested by the worm. Thus, caenopore-5 appears to contribute to the nutrition of the worm while simultaneously protecting the organism against pathogens. Here, three-dimensional heteronuclear NMR spectroscopy was used to solve the solution structure of caenopore-5. The NMR data revealed that two conformers of caenopore-5 exist in solution which differ by the isomerization of the peptide bond of Pro-81. The overall structure of the two caenopore-5 conformers consists of five amphiphatic helices connected by three disulfide bonds. The five helices are arranged in a folded leaf which is the characteristic signature of the SAPLIP family. The structure presented here is the first of an effector protein of the defensive system elucidated for the well-known model organism C. elegans.