title: Infestin, a thrombin inhibitor presents in Triatoma infestans midgut, a Chagas' disease vector: gene cloning, expression and characterization of the inhibitor.
abstract: This work describes the purification, gene cloning and expression of infestin, a thrombin inhibitor from midguts of Triatoma infestans. Infestin is located in the midgut and its purification was performed by anion-exchange and affinity chromatographies. The N-terminal sequence and the sequence of tryptic peptides were determined. Using RT-PCR, total RNA and infestin cDNA information, a DNA fragment was cloned which encodes a multi non-classical Kazal-type serine protease inhibitor. Isolated native infestin has two non-classical Kazal-type domains and shows an apparent molecular mass of 13 kDa, while its gene codes for a protein with four non-classical Kazal-type domains corresponding to an apparent molecular mass of 22 kDa. Two recombinant infestins, r-infestin 1-2 and r-infestin 1-4, were constructed using the vector pVT102U/alpha and expressed in S. cerevisiae. Native and r-infestin 1-2 showed very similar inhibitory activities towards thrombin and trypsin with dissociation constants of 43.5 and 25 pM for thrombin and 2.0 and 3.1 nM for trypsin, respectively. No other serine protease of the blood coagulation cascade was inhibited by the r-infestin 1-2. Surprisingly, r-infestin 1-4 inhibited not only thrombin and trypsin (K(i) of 0.8 and 5.2 nM, respectively), but also factor XIIa, factor Xa and plasmin (K(i) of 78 pM, 59.2 and 1.1 nM, respectively).
authors.affiliation: Departamento de Bioquímica, Escola Paulista de Medicina, UNIFESP-EPM, Sco Paulo, SP, Brazil.
authors.forename: I T N
authors.initials: IT
authors.lastname: Campos
authors.forename: R
authors.initials: R
authors.lastname: Amino
authors.forename: C A M
authors.initials: CA
authors.lastname: Sampaio
authors.forename: E A
authors.initials: EA
authors.lastname: Auerswald
authors.forename: T
authors.initials: T
authors.lastname: Friedrich
authors.forename: H-G
authors.initials: HG
authors.lastname: Lemaire
authors.forename: S
authors.initials: S
authors.lastname: Schenkman
authors.forename: A S
authors.initials: AS
authors.lastname: Tanaka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D014355:Chagas Disease; D003001:Cloning, Molecular; D004064:Digestive System; D015870:Gene Expression; D017344:Genes, Insect; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism; D007303:Insect Vectors; D008969:Molecular Sequence Data; D015842:Serine Proteinase Inhibitors / Q000235:genetics* / Q000378:metabolism; D013917:Thrombin / Q000037:antagonists & inhibitors*; D014224:Triatoma / Q000235:genetics*
chemical_list: D019476:Insect Proteins; D015842:Serine Proteinase Inhibitors; C467902:infestin protein, Triatoma infestans; D013917:Thrombin