What is the Difference Between Kinesin and Myosin

The main difference between kinesin and myosin is that the kinesin moves on microtubules while the myosin moves on microfilaments. Furthermore, kinesin, along with dynein, especially form the mitotic spindle while myosin forms both the cytoskeleton and the contractile filaments of the muscle cells. 

Kinesin, dynein, and myosin are the three types of motor proteins found in the cytoskeleton of animal cells. They use ATP energy of the cell to mediate various types of cellular movements. 

Key Areas Covered 

1. What is Kinesin
     – Definition, Motor Domains, Role
2. What is Myosin
     – Definition, Types, Role
3. What are the Similarities Between Kinesin and Myosin
     – Outline of Common Features
4. What is the Difference Between Kinesin and Myosin
     – Comparison of Key Differences

Key Terms 

Actin, Dynein, Kinesin, Microfilaments, Microtubules, Motor Proteins, Myosin

What is Kinesin 

Kinesin is the type of motor protein that uses microtubules as their tracks to move molecules throughout the cell. It contains two light and two heavy chains per molecule. Each heavy chain contains a globular head, which is capable of hydrolyzing ATP. These head regions serve as motor domains. Therefore, kinesin uses the chemical energy of ATP to exert their mechanical work. For instance, the direction of occurrence of the motor domain in the kinesin determines the direction of transport. Hence, kinesins with their motor domains in the N-terminal region move the cargo towards the (+) end of the microtubule. In opposition, the kinesins with their motor domains in the C-terminal region move the cargo towards the (-) end of the microtubule. 

Figure 1: Kinesin Movement

The main function of kinesin is to form the spindle apparatus during both mitosis and meiosis. Additionally, it shuttles cellular organelles like mitochondria, Golgi apparatus as well as vesicles.  

What is Myosin 

Myosin is another type of motor protein that uses microfilaments as their tracks to move molecules throughout the cell. It belongs to a superfamily of actin. Myosin also generates energy for the movement by hydrolyzing ATP. Different families of myosin have different functions inside the cell. Myosin II is the first identified myosin and it has two light chains and two heavy chains with motor domains. It moves towards the (+) end of the microfilament. The myosin II motor proteins are responsible for muscular contraction. The non-muscle myosin II is responsible for cell division during cytokinesis.  

Figure 2: Myosin Associated Actin

Another type of myosin called myosin V is responsible for organelle and vesicle transport. Myosin XI is responsible for cytoplasmic streaming.  

Similarities Between Kinesin and Myosin 

• Kinesin and myosin are two types of motor proteins found in animal cells. 
• Both are involved in the formation of the cytoskeleton. 
• Also, they are responsible for various types of cellular movements. 
• Additionally, both molecules are responsible for the active transport of molecules including carbohydrates, proteins, and fats.  
• Furthermore, the ATP powers their action. 
• And, both can move on a suitable substrate. 

Difference Between Kinesin and Myosin 

Definition 

Kinesin refers to an ATPase similar to dynein that functions as a motor protein in the intracellular transport especially of cell organelles and molecules (as mitochondria and proteins) along microtubules. Myosin refers to a fibrous protein which forms (together with actin) the contractile filaments of muscle cells, in addition to involving in motion in other types of cell. Thus, these definitions explain the fundamental difference between kinesin and myosin.

Type of Filaments 

The main difference between kinesin and myosin is that kinesin moves along microtubules of the cytoskeleton while myosin moves along the actin microfilaments.  

Role 

Kinesin is important for the formation of the spindle apparatus while myosin is important for cell motility, cell division, and muscular contractions. Hence, this is another difference between kinesin and myosin.

Conclusion 

Kinesin is a type of motor protein, which moves along microtubules with their cargo. It especially involves the formation of the spindle apparatus. On the other hand, myosin is another type of motor protein. It moves along the actin microfilaments. Generally, myosin is responsible for the muscular contractions and cell motility. Therefore, the main difference between kinesin and myosin is the type of molecular tracks they use for the movement and their role.

Reference:

1. Stenoien DL, Brady ST. Molecular Motors: Kinesin, Dynein and Myosin. In: Siegel GJ, Agranoff BW, Albers RW, et al., editors. Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. Philadelphia: Lippincott-Raven; 1999. Available Here

Image Courtesy:

1. “Actin kinesin walking” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia  
2. “Actin-myosin” By Jeff16 – Own work (CC BY-SA 4.0) via Commons Wikimedia