A family of motor proteins that play essential roles in muscle contraction, cell movement, and intracellular transport through their interaction with actin filaments and ATP.

Myosin

Myosin represents a large superfamily of motor proteins that convert chemical energy from ATP into mechanical force. These remarkable molecular machines are fundamental to numerous cellular processes and are particularly well-known for their role in muscle contraction.

Structure and Components

The typical myosin molecule consists of:

Head domain (motor domain)
- Contains the ATP site
- Features the actin-binding region
- Responsible for force generation
Neck region
- Contains binding sites for light chains
- Acts as a lever arm during movement
- Amplifies conformational changes
Tail domain
- Varies among myosin classes
- Enables cargo binding and specificity
- Facilitates protein-protein interactions

Classification

Scientists have identified over 35 classes of myosin, with key varieties including:

Myosin II (Conventional myosin)
- Primary type in skeletal muscle
- Forms thick filaments
- Essential for muscle contraction
Unconventional myosins
- Myosin V (vesicle transport)
- Myosin I (membrane tension)
- Myosin VI (endocytosis)

Cellular Functions

Muscle Contraction

In muscle cells, myosin II molecules form thick filaments that interact with thin filaments through the sliding filament theory. This interaction drives muscle contraction through the cross-bridge cycle.

Non-muscle Roles

Regulation

Myosin activity is regulated through multiple mechanisms:

Clinical Significance

Mutations in myosin genes can lead to various disorders:

Research Applications

Understanding myosin has led to developments in:

Drug development targeting muscle disorders
Nanotechnology applications
Biotechnology tools
Cell motility studies

The continuing study of myosin provides crucial insights into cellular mechanics and potential therapeutic targets for various diseases.