title: A heme-binding aspartic proteinase from the eggs of the hard tick Boophilus microplus.
abstract: An aspartic proteinase that binds heme with a 1:1 stoichiometry was isolated and cloned from the eggs of the cattle tick Boophilus microplus. This proteinase, herein named THAP (tick heme-binding aspartic proteinase) showed pepstatin-sensitive hydrolytic activity against several peptide and protein substrates. Although hemoglobin was a good substrate for THAP, low proteolytic activity was observed against globin devoid of the heme prosthetic group. Hydrolysis of globin by THAP increased as increasing amounts of heme were added to globin, with maximum activation at a heme-to-globin 1:1 ratio. Further additions of heme to the reaction medium inhibited proteolysis, back to a level similar to that observed against globin alone. The addition of heme did not change THAP activity toward a synthetic peptide or against ribonuclease, a non-hemeprotein substrate. The major storage protein of tick eggs, vitellin (VT), the probable physiological substrate of THAP, is a hemeprotein. Hydrolysis of VT by THAP was also inhibited by the addition of heme to the incubation media. Taken together, our results suggest that THAP uses heme bound to VT as a docking site to increase specificity and regulate VT degradation according to heme availability.
authors.affiliation: Departamento de Bioquimica Médica, Instituto de Ciências Biomédicas, Centro de Ciências da Saúde, Universidade Federal do Rio de Janeiro-RJ, Brazil. Sorgine@bioqmed.ufrj.br
authors.forename: M H
authors.initials: MH
authors.lastname: Sorgine
authors.forename: C
authors.initials: C
authors.lastname: Logullo
authors.forename: R B
authors.initials: RB
authors.lastname: Zingali
authors.forename: G O
authors.initials: GO
authors.lastname: Paiva-Silva
authors.forename: L
authors.initials: L
authors.lastname: Juliano
authors.forename: P L
authors.initials: PL
authors.lastname: Oliveira
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D004527:Egg Proteins / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D019476:Insect Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D008969:Molecular Sequence Data; D011817:Rabbits; D013987:Ticks / Q000201:enzymology*
chemical_list: D004527:Egg Proteins; D019476:Insect Proteins; D006418:Heme; D016282:Aspartic Acid Endopeptidases