Biology Motivation

Myosin proteins are responsible for all muscle movement. Muscle cells contain parallel arrays of actin microfilaments and myosin proteins [5]. The myosin proteins have a lever arm with a pair of catalytic heads extending out towards a parallel actin filament. By hydrolyzing a molecule of ATP, the myosin arm binds to the actin filament and then rotates through an angle, in a motion similar to an oar stroke, pulling the actin filament by around 10 nm. After each pull, the myosin arm detaches from the actin filament so that it does not interfere with the pull of the other myosin proteins and then recocks for another stroke. The combination of small pulls by myosin arms along the length of the cell moves the actin and myosin filaments parallel to each other, contracting the muscle fiber. This contraction is responsible for all macroscopic motion of animals [20]. Kinesin proteins are the transportation system for the interior of a cell. They move a variety of cargos along microtubules. These cargos include organelles, proteins for secretion, RNA, and the mitotic spindle during mitosis. During cellular mitosis, Dynein proteins move chromosomes [12]. Dynein proteins are also responsible for the motion of cilia and flagella [5]. The exact method by which proteins produce motion is not well understood, but some theories have been proposed. It is known that all of the proteins go through a catalytic cycle involving the breakdown of ATP. The main components of this cycle involve: the protein binding to a molecule of ATP, binding to an actin filament or microtubule, splitting the ATP into an adenosine diphosphate molecule and an inorganic phosphate molecule, moving some portion of the protein through a distance, releasing the two product molecules, and releasing the bond to the structural fiber. However, not all proteins proceed through this cycle in the same order [20]. The most prevalent theory holds that the cycle of ATP binding and hydrolysis create strain in the protein that produces motion when it is relieved. The strain appears to be produced in a spring-like coiled segment called an alpha helix. A lever arm called the neck linker amplifies this strain into the several nanometer motion of the protein [8]. An array of protein segments called switches is needed to coordinate binding and release of the microtubule or filament with motion and the ATP cycle [20]. Because so little is known about these proteins, they are an active topic of research. Understanding these proteins is important for a variety of reasons. Chromosomal non-disjunction diseases, like Down Syndrome, could be caused by a malfunction in these proteins. Disruption of normal functioning of kinesin interferes with development which causes defects, and interferes with cardiovascular and neurological function [20]. Because cancer cells divide frequently and kinesin and dynein proteins are necessary for cellular division, drugs that interfered with kinesin or dynein function could be effective chemotherapeutic agents [14]. Motor proteins are the smallest known mechanism for converting chemical energy to mechanical work, and more efficient than most macroscale motors. Understanding how these proteins work could also allow the production of biomemetic, nanoscale, motile robots. Far from a simple process, the eight-nanometer step of a molecular motor protein relies on complex interactions between hundreds of thousands of atoms, and helps provide organization for the great complexity of life.