Sandbox Reserved 1407

From Proteopedia

This Sandbox is Reserved from January through July 31, 2018 for use in the course HLSC322: Principles of Genetics and Genomics taught by Genevieve Houston-Ludlam at the University of Maryland, College Park, USA. This reservation includes Sandbox Reserved 1311 through Sandbox Reserved 1430.

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1 Heavy Meromyosin
2 Organism of Origin
3 Protein Structure
4 Function
5 Significance
6 References

Heavy Meromyosin

This is .

Heavy meromyosin, “mero” meaning “part of” is a part of the actin-myosin system that makes us sarcomeres, or muscle fibers. Heavy meromyosin and light meromyosin are subunits of myosin, which are formed by proteolysis, the breakdown of proteins. LMM is the long, straight portion in the “tail” region, whereas HMM is at the other end of the chain called the head portion.

Organism of Origin

This protein originated in tarantulas, Red Junglefowls and humans.

Protein Structure

Heavy meromyosin (HMM) is a subunit of myosin. There are two fragments that make up HMM: S-1 and S-2. S-1 projects out on an angle whereas S-2 is comprised of globular heads that can bind to actin. Together, these are called a myosin cross bridge. There are four distinct macromolecules that comprise HMM, including (196 amino acids: magenta), (150 amino acids: blue), (971 amino acids: gold), and (973 amino acids: purple).

Function

Heavy meromyosin is a part of the actin-myosin system. Heavy meromyosin (and light meromyosin) are subunits of myosin. HMM is the globular head portion of myosin which determines the rate of muscle contraction in an organism. Actin binding capacity and ATPase activity are dependent on HMM.

The sarcomere consists of thin and thick filaments. The thin filaments are made of actin while the thick filaments are myosin. Actin is blocked by tropomyosin, which prevents muscles from contracting. In order to contract, Ca2+ binds to troponin to move tropomyosin, so the myosin binding sites on actin are now open. When this is exposed, myosin will bind to actin only IF it is has been primed with ATP.

The ATP binding site is located on the HMM component of myosin, particularly in the S-1 subunit where the globular head that attached to actin is located. The ability and rate at which ATP binds here determines whether or not myson can bind to actin. When ATP is broken down into ADP and an inorganic phosphate, it releases the energy required for myosin to bind to actin. This thereby determines the rate of muscle contraction.

Without the S-1 subunit, there wouldn’t be any energy to power this reaction. The S-1 subunit also contains the actin-binding site. The globular head of HMM is where myosin binds to actin. This pulls the actin filaments and shrinks the sarcomere. This sliding process repeats until the muscle is completely contracted.

Significance

Heavy meromyosin is important for muscle contractions in a multitude of organisms. It plays an important role in microtubule-based movement as a part of the myosin complex. The ability for myosin to bind to actin and use ATP to create mechanical energy is dependent on heavy meromyosin. Without this protein, muscle contraction and mobility would be limited.