Human prostasomes express glycolytic enzymes with capacity for ATP production

Prostasomes are prostate-derived, exosome-like microvesicles that transmit signaling complexes between the acinar epithelial cells of the prostate and sperm cells. The vast majority of prostasomes have a diameter of 30-200 nm, and they are generally surrounded by a classical membrane bilayer. Using a selected proteomic approach, it became increasingly clear that prostasomes harbor distinct subsets of proteins that may be linked to adenosine triphosphate (ATP) metabolic turnover that in turn might be of importance in the role of prostasomes as auxiliary instruments in the fertilization process. Among the 21 proteins identified, most of the enzymes of anaerobic glycolysis were represented, and three of the glycolytic enzymes present are among the top 10 proteins found in most exosomes, once again linking prostasomes to the exosome family. Other prostasomal enzymes involved in ATP turnover were adenylate kinase, ATPase, 5'-nucleotidase, and hexose transporters. The identified enzymes in their prostasomal context were operational for ATP formation when supplied with substrates. The net ATP production was low due to a high prostasomal ATPase activity that could be partially inhibited by vanadate that was utilized to profile the ATP-forming ability of prostasomes. Glucose and fructose were equivalent as glycolytic substrates for prostasomal ATP formation, and the enzymes involved were apparently surface located on prostasomes, since an alternative substrate not being membrane permeable (glyceraldehyde 3-phosphate) was operative, too. There is no clear-cut function linked to this subset of prostasomal proteins, but some possible roles are discussed.