Proteomics of sperm duct and spermatophore from the ornate spiny lobster, Panulirus ornatus: identifying the precursor of adipokinetic hormone/corazonin-like peptide (ACP).

The adipokinetic hormone/corazonin-like peptide (ACP) functions as a hormone in many arthropod species. The ACP-encoding transcript is expressed in the neural tissues and sperm duct of the ornate spiny lobster, Panulirus ornatus, a species of importance to the aquaculture industry. In this study, the presence of the ACP precursor peptide was verified in the medial sperm duct and spermatophore of P. ornatus through peptide fragments identified by proteomic analysis. We examined the proteome of three tissues: the medial sperm duct, its spermatophoric contents, and a deposited 'tarspot', identifying other proteins involved with multiple functions including immune response, amelioration of oxidative stress, antimicrobial action, energy usage, and muscle function. To understand a potential role for ACP precursor peptides in these tissues, a screen targeting nine bacterial strains was carried out however no antimicrobial activity was found for ACP or related peptides. A 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to identify potential mild antioxidant activity in a peptide from the ACP precursor providing a putative function in the sperm duct. The histology of the medial sperm duct of P. ornatus, together with the protein constituents of the medial sperm duct, its contents, and tarspot are presented to provide a greater understanding of the male reproductive system of the ornate spiny lobster.