Adsorption mechanisms of microcystin variant conformations at water-mineral interfaces: A molecular modeling investigation.

Authors:
Amy L Pochodylo
Amy L Pochodylo
The Institute for Comparative and Environmental Toxicology
Thalia G Aoki
Thalia G Aoki
College of Agriculture and Life Sciences
College Station | United States
Dr. Ludmilla Aristilde, PhD
Dr. Ludmilla Aristilde, PhD
Cornell University
Associate Professor
Environmental Chemistry; Environmental Biochemistry; Environmental Engineering.
Ithaca, NY | United States

J Colloid Interface Sci 2016 Oct 9;480:166-174. Epub 2016 Jul 9.

The Institute for Comparative and Environmental Toxicology, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853, United States; Department of Biological and Environmental Engineering, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853, United States. Electronic address:

Microcystins (MCs) are potent toxins released during cyanobacterial blooms. Clay minerals are implicated in trapping MCs within soil particles in surface waters and sediments. In the absence of molecular characterization, the relevance of previously proposed adsorption mechanisms is lacking. Towards obtaining this characterization, we conducted Monte Carlo simulations combined with molecular dynamics relaxation of two MC variants, MC-leucine-arginine (MC-LR) and MC-leucine-alanine (MC-LA), adsorbed on hydrated montmorillonite with different electrolytes. The resulting adsorbate structures revealed how MC conformations and aqueous conditions dictate binding interactions at the mineral surface. Electrostatic coupling between the arginine residue and a carboxylate in MC-LR excluded the participation of arginine in mediating adsorption on montmorillonite in a NaCl solution. However, in a CaCl2 solution, the complexation of Ca by two carboxylate moieties in MC-LR changed the MC conformation, which allowed arginine to mediate electrostatic interaction with the mineral. By contrast, due to the lack of arginine in MC-LA, complexation of Ca by only one carboxylate in MC-LA was required to favor Ca-bridging interaction with the mineral. Multiple water-bridged H-bonding interactions were also important in anchoring MCs at the mineral surface. Our modeling results offer molecular insights into the structural and chemical factors that can control the fate of MCs at water-mineral interfaces.

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http://dx.doi.org/10.1016/j.jcis.2016.07.016DOI Listing
October 2016
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