Apelin is the peptide ligand for a class A G-protein coupled receptor (GPCR), denoted here as AR. The apelin-AR system has been shown to have roles in regulation of fluid homeostasis; angiogenesis during tumour formation; adipoinsular axis function; and in regulation of the cardiovascular system and central nervous system. Apelin is expressed as a 77-residue preproprotein which is truncated by various unidentified processing pathways to bioactive forms ranging from 13-36 residues, all of which include the extreme C-terminus of the preproprotein. Such a promiscuity in length of bioactive peptide, with forms at lengths from 13 to 36 residues observed in vivo, is highly unusual and may provide insight into the ability of the apelin-AR system to exert disparate physiological effects. Until now, no specific information is available about the processing pathway(s) involved in apelin production. We have cloned and expressed human proapelin, the C-terminal 55-residue component of preproapelin produced by postulated N-terminal signal peptide removal. This was produced in E. coli as a fusion protein with an N-terminal hexahistidine tag and TEV protease cleavage site suitable for affinity purification and high yield isolation following TEV protease cleavage. Proapelin is a highly basic peptide with multiple dibasic sites, any and all of which are potential sites of cleavage for the proprotein convertase (PC) class of enzymes. We present here a comprehensive structural and dynamics characterization of proapelin using CD, fluorescence and NMR spectroscopy. These findings are allowing us to probe the accessibility of the dibasic sites in proapelin to PC enzymes. This will facilitate the identification of the most likely PC enzymes involved in proapelin processing, allowing for direct validation by biochemical assays.