An atypical cysteine-type protein domain regulates cuticular extracellular matrix assembly in nematodes.

Apical extracellular matrices (aECMs) act as barriers against pathogens and shape tissue organization throughout animals. In nematodes, the cuticle is the aECM performing this function, representing a defining feature of this largest animal phylum. Morphological and molecular evidence supports that worm cuticles extend from the head into the mouth, the latter contributing to the large diversity of nematode feeding structures. However, the biochemical understanding of the compositions of nematode cuticles and head structures is largely limited to collagens. Here, we characterize a recently identified mucin-type protein DPY-6 as a constituent of the cuticle and mouth in the model organisms Pristionchus pacificus and Caenorhabditis elegans. Utilizing bioinformatic tools, we characterize an atypical sequence motif at the N-terminus of DPY-6, consisting of the residue pattern CxCxCxC embedded within a β-strand. We demonstrate through in vitro biophysical experiments that this cysteine motif facilitates the intermolecular dimerization of DPY-6 proteins. In vivo studies in both species reveal that this motif is involved in the proper localization of the protein in the cuticle, but functions synergistically with other protein domains in a species-specific manner. Given that dpy-6 transcriptomic expression precedes other cuticle components, we speculate that DPY-6 acts as a scaffold molecule for nematode cuticular aECM formation.