The neuro-endocrine X-organ sinus-gland complex regulates important crustacean physiological processes, such as growth, reproduction and molting. Its major products are the neuropeptides of the cHH/MIH/GIH family. Until now the structure-function relationships of these neuropeptides were established by sequence comparison. To study the functional relevance of conserved amino acid residues or peptide motifs, we generated point and deletion mutants of the Norway lobster Nephrops norvegicus cHH. The wild type mature neuropeptide cHH and its mutant forms were expressed in bacteria as fusion proteins and assayed in vivo to assess their hyperglycemic activity. The wild type cHH had a hyperglycemic activity similar to that of cHH present in an eyestalk extract, and it was blocked by an anti-recombinant cHH antibody. Bioassays of cHHs, obtained by a progressive deletion of five highly conserved motifs, showed that the only deleted cHH, which conserves a hyperglycemic activity, is the one lacking the C-terminal motif, but still retaining all the motifs reported to be important for functional specificity and three-dimensional structure. All the cHH point mutants lacked a hyperglycemic activity. These results identify amino acid residues that are required for the hyperglycemic activity of cHH.
