Molecular Motor Directional Movement Mechanism

With the development of new technology for probing and manipulating single molecular motor, such as optical tweezers technique, microneedles, microphotographics and optimal sensors, greet progress has been made in the molecular biology, especially in the studies of the structure and dynamics. Though there are hundreds of motors have been found which different in structure, they all can move along certain track in definite directions when they consume the free energy (usually be ATP)/electrochemical gradiment. According to the difference of their manners of movement, they are generally divided into two classes: one is linear motor including myosin, kinesin, dynesin, DNA helicase, the other is rotary motor, such as Fl-ATP ase and the bacterical flagellar motor. In this letter, we will simply introduce some kinds of motors well known by people and discuss their structure, dynamic characteristic and their importance in life process. Comparing lots of biochemical experiments of myosin and kinesin, we find every kind of motor has a "catalytic core" which binding ATP and track in its domain and "neck linker" which closely connected with dynamic motion. Studying the structure of motor enable us to understand its mechanism of directed movement.As molecular motor lies in liquid environment, it can be regarded as Brownian particles or Brownian rachet in physics, and its motion can be classified into theoretical frame of Brownian movement, analyzed and calculated by Langenvin equation or Fokker-Plank equation in nonequilibrium statistical physics. While random fluctuating, molecular motor occurs a series of periodic chemical reactions (such as the binding of ATP, the subsequent hydrolysis, and the release of the products of the hydrolysis) and conformational changes that result in the changes of interaction between motors and its track. The joint action of these factors makemotors move unidirectionally on the basis of random fluctuation (i.e. the current). Studying unidirectional motion mechanism of molecular motor is studying the current. The minimum information required to make a complete model is 1) the values of the rate constants for nonmechanical processes, and 2) estimates of the shape of the one-dimensional potential energy function V(s), for mechanical steps. We will introduce two typical models in this article: one is the directed movement of the Brownian particle generated by two fluctuating potentials, the other is the Brownian motor possessing internal degree of freedom, in which the track consists of a line of small identical ball, motor and its track are view as dipoles, and the dominant interaction between them is electric. Supposing that the change of the interaction is represented by the rotation of its internal degree continuousely , we can evaluate the current explicitly by means of matrix continued fraction technique.In order to cqrrespond with biological motors as more as possible, a new model is put forward on the basis of Brownian motors possessing internal degree of freedom. Assume that the orintation of the internal dipole transit between two discrete states, and the track is flat, we calculate the numerical solution of the current by means of spacial discretization. Discussing the affects on the current induced by thermal strength and jump rates, we find there are certain intervals in which the values of the current are larger, and different jump rates can cause the reversion of the current.