Canavalia ensiformis urease, Jaburetox and derived peptides form ion channels in planar lipid bilayers

Abstract

Ureases catalyze the hydrolysis of urea into NH3 and CO2. They are synthesized by plants, fungi and bacteria but not by animals. Ureases display biological activities unrelated to their enzymatic activity, i.e., platelet and neutrophil activation, fungus inhibition and insecticidal effect. Urease from Canavalia ensiformis (jack bean) is toxic to several hemipteran and coleopteran insects. Jaburetox is an insecticidal fragment derived from jack bean urease. Among other effects, Jaburetox has been shown to interact with lipid vesicles. In this work, the ion channel activity of C. ensiformis urease, Jaburetox and three deletion mutants of Jaburetox (one lacking the N-terminal region, one lacking the C-terminal region and one missing the central β-hairpin) were tested on planar lipid bilayers. All proteins formed well resolved, highly cation-selective channels exhibiting two conducting states whose conductance ranges were 7-18pS and 32-79pS, respectively. Urease and the N-terminal mutant of Jaburetox were more active at negative potentials, while the channels of the other peptides did not display voltage-dependence. This is the first direct demonstration of the capacity of C. ensiformis urease and Jaburetox to permeabilize membranes through an ion channel-based mechanism, which may be a crucial step of their diverse biological activities, including host defense.

Jaburetox: update on a urease-derived peptide

“…The ability of these peptides to form ion channels in lipid bilayers was also confirmed by testing with planar lipid bilayers (PLB) [15]. In this study, it was shown that the peptide, as well as the above mentioned mutants can insert themselves into planar lipid bilayers and form cation selective ion channels.…”

“…Barros et al [38] observed that JBTX was able to permeabilize acidic liposomes to release entrapped carboxy-fluorescein. Piovesan et al [15] reported that JBTX, as well as some of its truncated mutants, was capable of inserting itself into neutral planar lipid bilayers forming cation-selective ion channels. More recently, Micheletto et al [39] studied by small angle X-ray scattering (SAXS) the interaction among JBTX and multilamellar liposomes with a lipid composition typical of human platelets membrane.…”

Pliable natural biocide: Jaburetox is an intrinsically disordered insecticidal and fungicidal polypeptide derived from jack bean urease

“…Considering the membrane-disturbing properties of Jaburetox [19,23,24], we would expect that the polypeptide would change its conformation to a folded state when in contact with membranes. The full assignment of Jaburetox reported here will allow us to perform NMR studies of this toxic polypeptide in contact with lipid micelles mimicking insect and fungus membranes [78], determining changes in its conformation properties based on modifications of the 1 H-15 N HSQC spectrum.…”

“…Other studies have demonstrated that Jaburetox and its mutants can form wellresolved, highly cation-selective channels. The peptide corresponding to the N-terminal part of Jaburetox is more active in negative potentials, while the ion-channel activity of Jaburetox and the other mutants do not display voltage dependence [24].…”

Milled legume grain as urease source for the ammonization of elephant grass hay

“…2017 DOI: 10.1590/S0100-204X2017001200016 microorganisms to carbohydrates; and improves digestibility by changing fiber structure (Wanapat et al, 2009;Polyorach & Wanapat, 2015). Soybean (Medeiros-Silva et al, 2014) and jack bean (Piovesan et al, 2014) are common urease sources. Other legumes like pigeon pea, however, also contain this enzyme (Balasubramanian et al, 2013).…”