Browsing by Author "Preto, Jordane"
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Item Investigation of the electrical properties of microtubule ensembles under cell-like conditions(2020) Aarat, Kalra P.; Patel, Sahil D.; Bhuiyan, Asadullah; Preto, Jordane; Scheuer, Kyle G.; Mohammed, Usman; Lewis, John D.; Rezania, Vahid; Shankar, Karthik; Tuszynski, Jack A.Microtubules (MTs) are cylindrical polymers composed of the heterodimers of protein α, β- tubulin that play a variety of well-recognised intracellular roles, such as maintaining the shape and rigidity of the cell, aiding in positioning and stabilisation of the mitotic spindle for allowing chromosomal segregation, acting as ‘rails’ for macromolecular transport and forming cilia and flagella for cell movement. Since the tubulin dimer possesses a high negative electric charge of ~23e and a large intrinsic high dipole moment of approximately 1750 D [1,2], MTs have been implicated in electrically-mediated biological roles [3,4,5,6]. They have been modelled as nanowires capable of enhancing ionic transport [7,8], and simulated to receive and attenuate electrical oscillations [4,9,10,11]. In solution, MTs have been shown to align with applied electric fields [2,12,13,14,15,16]. Recently, MTs have also been modelled as the primary cellular targets for low-intensity (1–2 V), intermediate-frequency (100–300 kHz) electric fields termed TTFields (tumour-treating electric fields) that inhibit cancer cell proliferation, in particular glioma [17,18,19]. Indeed, MTs have been reported to decrease buffer solution resistance [12,13], leading to a conductance peak at frequencies close to the TTField regime [20]. While these studies show that MTs are highly sensitive to external electric fields, answers to the questions ‘How do MTs effect a solution’s capacitance?’ and ‘What is the capacitance of a single MT?’ are still elusive and crucial to the determination of the dielectric properties of living cells. The tubulin concentration in mammalian cells varies in the micromolar range (~10–25 μM) [21,22]. In vitro, polymerizing tubulin at such high concentrations can lead to the formation of entangled networks, confounding quantification of the individual MT response to electric fields. Electro-rotation, di-electrophoresis and impedance spectroscopy are thus performed using low concentrations of tubulin, in the nanomolar regime, to enable robust observation of individual MTs.Item Revealing and attenuating the electrostatic properties of tubulin and its polymers(2021) Kalra, Aarat P.; Patel, Sahil D.; Eakins, Boden B.; Riddell, Saralyn; Kumar, Pawan; Winter, Philip; Preto, Jordane; Carlson, Kris W.; Lewis, John D.; Rezania, Vahid; Tuszynski, Jack A.; Shankar, KarthikTubulin is an electrostatically negative protein that forms cylindrical polymers termed microtubules, which are crucial for a variety of intracellular roles. Exploiting the electrostatic behavior of tubulin and microtubules within functional microfluidic and optoelectronic devices is limited due to the lack of understanding of tubulin behavior as a function of solvent composition. This work displays the tunability of tubulin surface charge using dimethyl sulfoxide (DMSO) for the first time. Increasing the DMSO volume fractions leads to the lowering of tubulin's negative surface charge, eventually causing it to become positive in solutions >80% DMSO. As determined by electrophoretic mobility measurements, this change in surface charge is directionally reversible, i.e., permitting control between −1.5 and + 0.2 cm2 (V s)−1. When usually negative microtubules are exposed to these conditions, the positively charged tubulin forms tubulin sheets and aggregates, as revealed by an electrophoretic transport assay. Fluorescence-based experiments also indicate that tubulin sheets and aggregates colocalize with negatively charged g-C3N4 sheets while microtubules do not, further verifying the presence of a positive surface charge. This study illustrates that tubulin and its polymers, in addition to being mechanically robust, are also electrically tunable.