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Adsorption of Insecticidal Cry1Ab Protein to Humic Substances. 1. Experimental Approach and Mechanistic Aspects
journal contribution
posted on 2012-09-18, 00:00 authored by Michael Sander, Jeanne E. Tomaszewski, Michael Madliger, René
P. SchwarzenbachAdsorption is a key process affecting the fate of insecticidal
Cry proteins (Bt toxins), produced by genetically
modified Bt crops, in soils. However, the mechanisms
of adsorption to soil organic matter (SOM) remain poorly understood.
This work assesses the forces driving the adsorption of Cry1Ab to
Leonardite humic acid (LHA), used as a model for SOM. We studied the
effects of solution pH and ionic strength (I) on
adsorption using a quartz crystal microbalance with dissipation monitoring
and optical waveguide lightmode spectroscopy. Initial Cry1Ab adsorption
rates were close to diffusion-limited and resulted in extensive adsorption,
even at pH >6, at which LHA and Cry1Ab carry negative net charges.
Adsorption increased with decreasing I at pH >6,
indicating Cry1Ab–LHA patch-controlled electrostatic attraction
via positively charged domains of Cry1Ab. Upon rinsing, only a fraction
of Cry1Ab desorbed, suggesting a range of interaction energies of
Cry1Ab with LHA. Different interaction energies likely resulted from
nonuniformity in the LHA surface polarity, with higher Cry1Ab affinities
to more apolar LHA regions due to the hydrophobic effect. Contributions
from the hydrophobic effect were substantiated by comparison of the
adsorption of Cry1Ab and the reference proteins albumin and lysozyme
to LHA and to apolar and polar model surfaces.
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apolar LHA regionsDifferent interaction energiesCry 1Ab affinitiesInitial Cry 1Ab adsorption ratesinsecticidal Cry proteinsquartz crystal microbalanceCry 1Ab desorbedreference proteins albuminLeonardite humic acidCry 1AbLHA surface polarityInsecticidal Cry 1Ab ProteinSOMwaveguide lightmode spectroscopy
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