Abstract
Optical tweezers have enabled the exploration of picoNewton forces and dynamics in single–molecule systems such as DNA and molecular motors. In this work, we used optical tweezers to study the folding/unfolding dynamics of the APTSTX1–aptamer, a single-stranded DNA molecule with high affinity for saxitoxin (STX), a lethal neurotoxin. By measuring the transition force during (un)folding processes, we were able to characterize and distinguish the conformational changes of this aptamer in the presence of magnesium ions and toxin. This work was supported by molecular dynamics (MD) simulations to propose an unfolding mechanism of the aptamer–Mg+2 complex. Our results are a step towards the development of new aptamer-based STX sensors that are potentially cheaper and more sensitive than current alternatives.
Highlights
Harmful algal blooms contain toxins that, when bio-accumulated by bivalve molluscs, can be fatal upon human consumption
In order to characterize the structure of the STX aptamer with optical tweezers, we observed that after 132 pulling experiments of a single APTSTX1 aptamer under phosphate buffer solution (PBS)–buffer–only, control conditions (CNT), 71.2% of the cases did not present folding or unfolding (Fig 2 Control; a representative curve is shown in S2 Fig)
SMD simulations correlated very well with the clustered contour length at lower extension obtained by optical tweezers
Summary
Harmful algal blooms contain toxins that, when bio-accumulated by bivalve molluscs, can be fatal upon human consumption. Among these toxins, saxitoxin (STX) is dangerous due to its binding-affinity to sodium channels in voltage-excitable cells [1]. STX causes asphyxia from diaphragm paralysis in less than an hour, with a lethal oral dose in humans as low as 1–4 mg [2]. STX concentrations are monitored regularly by injecting mice with a shellfish extract and measuring their time of death [3, 4]. Other methods of STX detection are available, they require expensive equipment and lack the robustness and sensitivity of the mouse bioassay [3, 5,6,7].
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