title: A plant Kunitz-type inhibitor mimics bradykinin-induced cytosolic calcium increase and intestinal smooth muscle contraction.
abstract: BbKI is a kallikrein inhibitor with a reactive site sequence similar to that of kinins, the vasoactive peptides inserted in kininogen moieties. This structural similarity probably contributes to the strong interaction with plasma kallikrein, the enzyme that releases, from high-molecular weight kininogen (HMWK), the proinflammatory peptide bradykinin, which acts on B(2) receptors (B(2)R). BbKI was examined on smooth muscle contraction and Ca(2+) mobilization, in which the kallikrein-kinin system is involved. Contrary to expectations, BbKI (1.8 μm) increased [Ca(2+)](c) and contraction, as observed with BK (2.0 μm). Not blocked by B(1) receptors (B(1)R), the BbKI agonistic effect was blocked by the B(2)R antagonist, HOE-140 (6 μm), and the involvement of B(2)R was confirmed in B(2)R-knockout mice intestine. The same tissue response was obtained using a synthetic peptide derived from the BbKI reactive site structure, more resistant than BK to angiotensin I-converting enzyme (ACE) hydrolysis. Depending on the concentration, BbKI has a dual effect. At a low concentration, BbKI acts as a potent kallikrein inhibitor; however, due to the similarity to BK, in high concentrations, BbKI greatly increases Ca(2+) release from internal storages, as a consequence of its interaction with B(2)R. Therefore, the antagonistic and agonistic effects of BbKI may be considered in conditions of B(2)R involvement.
authors.affiliation: Department of Biochemistry, Escola Paulista de Medicina, Universidade Federal de São Paulo, Rua Três de Maio 100, 04044-020 São Paulo, SP, Brazil.
authors.forename: Sheila Siqueira
authors.initials: SS
authors.lastname: Andrade
authors.forename: Soraya Soubhi
authors.initials: SS
authors.lastname: Smaili
authors.forename: Priscila Totarelli
authors.initials: PT
authors.lastname: Monteforte
authors.forename: Antônio
authors.initials: A
authors.lastname: Miranda
authors.forename: Maria
authors.initials: M
authors.lastname: Kouyoumdjian
authors.forename: Misako Uemura
authors.initials: MU
authors.lastname: Sampaio
authors.forename: Guiomar Silva
authors.initials: GS
authors.lastname: Lopes
authors.forename: Maria Luiza V
authors.initials: ML
authors.lastname: Oliva
mesh_terms: D000818:Animals; D036481:Bauhinia / Q000737:chemistry; D001665:Binding Sites; D001920:Bradykinin / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D065094:Bradykinin B2 Receptor Antagonists; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004347:Drug Interactions; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects / Q000502:physiology*; D007610:Kallikreins / Q000037:antagonists & inhibitors; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010455:Peptides / Q000737:chemistry* / Q000494:pharmacology*; D010940:Plant Proteins / Q000737:chemistry* / Q000494:pharmacology*; D017208:Rats, Wistar; D043783:Receptor, Bradykinin B1 / Q000378:metabolism; D043782:Receptor, Bradykinin B2 / Q000378:metabolism; D014700:Verapamil / Q000494:pharmacology
chemical_list: D065094:Bradykinin B2 Receptor Antagonists; C053865:Kunitz-type protease inhibitor, plant; D010455:Peptides; D010940:Plant Proteins; D043783:Receptor, Bradykinin B1; D043782:Receptor, Bradykinin B2; C065679:icatibant; D014700:Verapamil; D007610:Kallikreins; D001920:Bradykinin; D002118:Calcium