Trialysin, a Novel Pore-forming Protein from Saliva of Hematophagous Insects Activated by Limited Proteolysis

Abstract

We have characterized a pore-forming lytic protein from the saliva of the hematophagous insect Triatoma infestans, a vector of Chagas disease. This protein, named trialysin, has 22 kDa and is present in the saliva at about 200 g/ml. Purified trialysin forms voltage-dependent channels in planar lipid bilayers with conductance of 880 ؎ 40 pS. It lyses protozoan parasites and bacteria indicating that it has a role in the control of microorganism growth in the salivary glands. At higher concentrations, but below those found in saliva, trialysin can also permeabilize and lyse mammalian cells, suggesting that it might also facilitate insect blood feeding by interfering with the cell response of the host. The translated cDNA sequence of trialysin shows a basic, lysine-rich protein in which the N-terminal region is predicted to form an amphipathic ␣-helical structure with positive charges on one side and hydrophobic amino acids on the opposite side. A synthetic peptide corresponding to this cationic amphipathic ␣-helix induces protozoan lysis and mammalian cell permeabilization, showing that this region is involved in lytic activity. However, the lytic peptide G6V32 is 10-fold less efficient than trialysin in lysing parasites and 100-fold less efficient in permeabilizing mammalian cells. Trialysin activity is about 10-fold reduced in salivary gland homogenates prepared in the presence of an irreversible serine-protease inhibitor. Since trialysin precursor contains an anionic pro-sequence of 33 amino acids contiguous to the cationic amphipathic putative ␣-helix, we propose that removal of the acidic pro-sequence by limited proteolysis activates trialysin by exposing this lytic basic amphipathic motif.

Trypanosoma rangeli interactions within the vector Rhodnius prolixus: a mini review

“…They concluded that T. infestans, which is refractory to infection by T. rangeli, appears to contain a much wider distribution of agglutinins and trypanolytic factors in its tissue than the susceptible species, R. prolixus. Amino et al (2002) characterized a pore-forming lytic protein from the saliva of T. infestans. This protein, named trialysin, lysed protozoan parasites and bacteria indicating that it plays a role in the control of microorganism growth in the salivary glands.…”

Preliminary characterization of a Rhodnius prolixus hemolymph trypanolytic protein, this being a determinant of Trypanosoma rangeli KP1(+) and KP1(-) subpopulations' vectorial ability

“…A lytic protein called "trialysin" has been detected in Triatoma infestans saliva which acts on T. cruzi trypomastigotes (Amino et al 2002). An antimicrobial peptide belonging to the family of small cationic peptides associated with innate immunity has been isolated from the R. prolixus hemolymph (López et al 2003).…”

“…Other peptides or proteins have also been found which are constitutively present in the hemolymph or different insect secretions, such as an antimicrobial peptide "stomoxyn" detected in Stomoxis calcitrans presenting lytic activity against T. brucei rhodesiense (Boulanger et al 2002a, b). A lytic protein called "trialysin" has been detected in Triatoma infestans saliva which acts on T. cruzi trypomastigotes (Amino et al 2002). An antimicrobial peptide belonging to the family of small cationic peptides associated with innate immunity has been isolated from the R. prolixus hemolymph (López et al 2003).…”

The structural molecular biology network of the State of São Paulo, Brazil

“…Among our studies, we have characterized a 22 kD pore forming protein, named trialysin, from saliva of T. infestans (Amino et al 2002). This protein contains on the N-terminus a sequence that predicts an amphipathic α-helix and its corresponding synthetic peptide retains cytolytic activity.…”