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Register a new userRecovery of state-specific potential of molecular motor from single-molecule trajectory
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We have developed a novel method to evaluate the potential profile of a molecular motor at each chemical state from only the probes trajectory and applied it to a rotary molecular motor F$_1$-ATPase. By using this method, we could also obtain the information regarding the mechanochemical coupling and energetics. We demonstrate that the position-dependent transition of the chemical states is the key feature for the highly efficient free-energy transduction by F$_1$-ATPase.
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Transport of intracellular cargo is often mediated by teams of molecular motors that function in a chaotic environment and varying conditions. We show that the motors have unique steady state behavior which enables transport modalities that are robust. Under reduced ATP concentrations, multi-motor configurations are preferred over single motors. Higher load force drives motors to cluster, but very high loads compel them to separate in a manner that promotes immediate cargo movement once the load reduces. These inferences, backed by analytical guarantees, provide unique insights into the coordination strategies adopted by motors.
In many intracellular processes, the length distribution of microtubules is controlled by depolymerizing motor proteins. Experiments have shown that, following non-specific binding to the surface of a microtubule, depolymerizers are transported to the microtubule tip(s) by diffusion or directed walk and, then, depolymerize the microtubule from the tip(s) after accumulating there. We develop a quantitative model to study the depolymerizing action of such a generic motor protein, and its possible effects on the length distribution of microtubules. We show that, when the motor protein concentration in solution exceeds a critical value, a steady state is reached where the length distribution is, in general, non-monotonic with a single peak. However, for highly processive motors and large motor densities, this distribution effectively becomes an exponential decay. Our findings suggest that such motor proteins may be selectively used by the cell to ensure precise control of MT lengths. The model is also used to analyze experimental observations of motor-induced depolymerization.
Single molecule tracking in live cells is the ultimate tool to study subcellular protein dynamics, but it is often limited by the probe size and photostability. Due to these issues, long-term tracking of proteins in confined and crowded environments, such as intracellular spaces, remains challenging. We have developed a novel optical probe consisting of 5-nm gold nanoparticles functionalized with a small fragment of camelid antibodies that recognize widely used GFPs with a very high affinity, which we call GFP-nanobodies. These small gold nanoparticles can be detected and tracked using photothermal imaging for arbitrarily long periods of time. Surface and intracellular GFP-proteins were effectively labeled even in very crowded environments such as adhesion sites and cytoskeletal structures both in vitro and in live cell cultures. These nanobody-coated gold nanoparticles are probes with unparalleled capabilities; small size, perfect photostability, high specificity, and versatility afforded by combination with the vast existing library of GFP-tagged proteins.
We present a study of the DNA translocation of the bacteriophage phi 29 packaging molecular motor. From the experimental available information we present a model system based in an stochastic fashing potential, which reproduces the experimental observations such as: detailed trajectories, steps and substeps, spatial correlation, and velocity. Moreover the model allows the evaluation of power and efficiency of this motor. We have found that the maximum power regime does not correspond with that of the maximum efficiency. These informations can stimulate further experiments.
This mini review focuses on conductance measurements through molecular junctions containing few tens of molecules, which are fabricated along two approaches: (i) conducting atomic force microscope contacting a self-assembled monolayers on metal surface, and (ii) tiny molecular junctions made of metal nanodot (diameter < 10 nm), covered by fewer than 100 molecules and contacted by a conducting atomic force microscope. In particular, this latter approach has allowed to obtain new results or to revisit previous ones, which are reviewed here: (i) how the electron transport properties of molecular junctions are modified by mechanical constraint, (ii) the role of intermolecular interactions on the shape of conductance histograms of molecular junctions, and (iii) the demonstration that a molecular diode can operate in the microwave regime up to 18 GHz.
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