title: Inorganic polyphosphate inhibits an aspartic protease-like activity in the eggs of Rhodnius prolixus (Stahl) and impairs yolk mobilization in vitro.
abstract: Inorganic polyphosphate (poly P) is a polymer of phosphate residues that has been shown to act as modulator of some vertebrate cathepsins. In the egg yolk granules of Rhodnius prolixus, a cathepsin D is the main protease involved in yolk mobilization and is dependent on an activation by acid phosphatases. In this study, we showed a possible role of poly P stored inside yolk granules on the inhibition of cathepsin D and arrest of yolk mobilization during early embryogenesis of these insects. Enzymatic assays detected poly P stores inside the eggs of R. prolixus. We observed that micromolar poly P concentrations inhibited cathepsin D proteolytic activity using both synthetic peptides and homogenates of egg yolk as substrates. Poly P was a substrate for Rhodnius acid phosphatase and also a strong competitive inhibitor of a pNPPase activity. Fusion events have been suggested as important steps towards acid phosphatase transport to yolk granules. We observed that poly P levels in those compartments were reduced after in vitro fusion assays and that the remaining poly P did not have the same cathepsin D inhibition activity after fusion. Our results are consistent with the hypothesis that poly P is a cathepsin D inhibitor and a substrate for acid phosphatase inside yolk granules. It is possible that, once activated, acid phosphatase might degrade poly P, allowing cathepsin D to initiate yolk proteolysis. We, therefore, suggest that degradation of poly P might represent a new step toward yolk mobilization during embryogenesis of R. prolixus.
authors: Laboratório de Entomologia Médica, Programa de Biologia Celular e Parasitologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, RJ, Brazil.
authors: F M
authors: FM
authors: Gomes
authors: D M P
authors: DM
authors: Oliveira
authors: L S
authors: LS
authors: Motta
authors: I B
authors: IB
authors: Ramos
authors: K M
authors: KM
authors: Miranda
authors: E A
authors: EA
authors: Machado
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000378:metabolism; D000135:Acid Phosphatase / Q000378:metabolism*; D000818:Animals; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004527:Egg Proteins / Q000378:metabolism*; D004530:Egg Yolk / Q000187:drug effects / Q000201:enzymology*; D019476:Insect Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010436:Pepstatins / Q000494:pharmacology; D011122:Polyphosphates / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D021381:Protein Transport; D011994:Recombinant Proteins / Q000378:metabolism; D012239:Rhodnius / Q000187:drug effects / Q000196:embryology / Q000201:enzymology*
chemical_list: D004527:Egg Proteins; D019476:Insect Proteins; D010436:Pepstatins; D011122:Polyphosphates; D011480:Protease Inhibitors; D011994:Recombinant Proteins; D000135:Acid Phosphatase; D002402:Cathepsin D; D017766:Acid Anhydride Hydrolases; C020137:exopolyphosphatase; C031375:pepstatin