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This volume examines a number of different molecular motors that utilize ATP. The molecular machines to be discussed include ATP synthase, myosin, kinesin, DNA helicases, DNA topoisomerases, chaperones and bacterial rotory motors. The discussion of these various molecular motors is rarely undertaken in one volume and will serve as a great resource for scientists studying structure and function of multiprotein complexes as well as those working on energy coupling mechanisms. The areas of research presented in this volume do not normally overlap, and yet they share common mechanisms. This volume examines a number of different molecular motors that utilize ATP. The molecular machines to be discussed include ATP synthase, myosin, kinesin, DNA helicases, DNA topoisomerases, chaperones and bacterial rotory motors. The discussion of these various molecular motors is rarely undertaken in one volume and will serve as a great resource for scientists studying structure and function of multiprotein complexes as well as those working on energy coupling mechanisms. The areas of research presented in this volume do not normally overlap, and yet they share common mechanisms.
Molecular motors convert chemical energy (typically from ATP hydrolysis) to directed motion and mechanical work. Biomolecular motors are proteins able of converting chemical energy into mechanical motion and force. Because of their dimension, the many small parts that make up molecular motors must operate at energies only a few times greater than those of the thermal baths. The description of molecular motors must be stochastic in nature. Their actions are often described in terms of Brownian Ratchets mechanisms. In order to describe the principles used in their movement, we need to use the tools that theoretical physics give us. In this book we centralize on the some physical mechanisms of molecular motors.
Biological systems abound with examples of molecular motors - biological machines for converting the chemical energy of ATP into mechanical movement by cells - they play pivotal roles in diverse cellular function.
In the living cell, the organization of the complex internal structure relies to a large extent on molecular motors. Molecular motors are proteins that are able to convert chemical energy from the hydrolysis of adenosine triphosphate (ATP) into mechanical work. Being about 10 to 100 nanometers in size, the molecules act on a length scale, for which thermal collisions have a considerable impact onto their motion. In this way, they constitute paradigmatic examples of thermodynamic machines out of equilibrium. This study develops a theoretical description for the energy conversion by the molecular motor myosin V, using many different aspects of theoretical physics. Myosin V has been studied extensively in both bulk and single molecule experiments. Its stepping velocity has been characterized as a function of external control parameters such as nucleotide concentration and applied forces. In addition, numerous kinetic rates involved in the enzymatic reaction of the molecule have been determined. For forces that exceed the stall force of the motor, myosin V exhibits a 'ratcheting' behaviour: For loads in the direction of forward stepping, the velocity depends on the concentration of ATP, while for backward loads there is no such influence. Based on the chemical states of the motor, we construct a general network theory that incorporates experimental observations about the stepping behaviour of myosin V. The motor's motion is captured through the network description supplemented by a Markov process to describe the motor dynamics. This approach has the advantage of directly addressing the chemical kinetics of the molecule, and treating the mechanical and chemical processes on equal grounds. We utilize constraints arising from nonequilibrium thermodynamics to determine motor parameters and demonstrate that the motor behaviour is governed by several chemomechanical motor cycles. In addition, we investigate the functional dependence of stepping rates on force by deducing the motor's response to external loads via an appropriate Fokker-Planck equation. For substall forces, the dominant pathway of the motor network is profoundly different from the one for superstall forces, which leads to a stepping behaviour that is in agreement with the experimental observations. The extension of our analysis to Markov processes with absorbing boundaries allows for the calculation of the motor's dwell time distributions. These reveal aspects of the coordination of the motor's heads and contain direct information about the backsteps of the motor. Our theory provides a unified description for the myosin V motor as studied in single motor experiments.
A Unified Microscopic Approach to Analyzing Complex Processes in Molecular MotorsMotor Proteins and Molecular Motors explores the mechanisms of cellular functioning associated with several specific enzymatic molecules called motor proteins. Motor proteins, also known as molecular motors, play important roles in living systems by supporting cellular
This book provides a comprehensive overview of biomotors (molecular motors) within the body with a specific concentration on revolving molecular motors. The bioengineering of these new revolving molecular motors will go a long way in creating machines that will be able to carry RNA and DNA drugs directly to diseased cells to destroy them. The book goes into specific details regarding the bioengineering, fabrication, synthesis, and future utilization of these devices for nanomedicine.
This volume examines a number of different molecular motors that utilize ATP. The molecular machines to be discussed include ATP synthase, myosin, kinesin, DNA helicases, DNA topoisomerases, chaperones and bacterial rotory motors. The discussion of these various molecular motors is rarely undertaken in one volume and will serve as a great resource for scientists studying structure and function of multiprotein complexes as well as those working on energy coupling mechanisms. The areas of research presented in this volume do not normally overlap, and yet they share common mechanisms. This volume examines a number of different molecular motors that utilize ATP. The molecular machines to be discussed include ATP synthase, myosin, kinesin, DNA helicases, DNA topoisomerases, chaperones and bacterial rotory motors. The discussion of these various molecular motors is rarely undertaken in one volume and will serve as a great resource for scientists studying structure and function of multiprotein complexes as well as those working on energy coupling mechanisms. The areas of research presented in this volume do not normally overlap, and yet they share common mechanisms.
Biological cells can harness the free energy of ATP hydrolysis to perform mechanical tasks using molecular motor proteins. These nanoscale machines are able to generate directional motion through mechanochemical cycles which rely on allosteric communication and large rearrangements of protein domains. In studies of molecular motors, protein engineering allows us to test our understanding of relationships between structure and function, while single-molecule methods allow us to directly observe motor dynamics. Here we consider two systems which undergo large conformational changes: cytoplasmic dynein and DNA gyrase. We use protein engineering to investigate structural features that contribute to dynein velocity and processivity. Building on our initial findings, we are able to design dynein motors that change speed in response to light. The speed and controllability of future designs may be improved with further engineering, in order to generate light-activatable, dynein-based tools which can be used to study transport functions in vivo. In the second half of this dissertation, we consider a single-molecule technique for multimodal measurements of mechanics and fluorescence in DNA and DNA:protein complexes. Mechanical measurements based on magnetic tweezers are combined with simultaneous fluorescence imaging that can report on macromolecular binding and local conformational changes. We outline how this method can be applied to study the mechanism of DNA gyrase, a motor which introduces negative supercoils by coordinating protein domain motions and ATP hydrolysis with DNA cleavage and religation. We observe binding coincident with mechanics and report on challenges in using FRET-labeled enzymes to correlate domain motions with mechanical substeps. We anticipate that correlative multimodal measurements will be valuable tools for characterizing the dynamics of DNA gyrase and other large nucleoprotein machines.