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.