Tropomyosin is a tetramer under physiological salt conditions
Ingrid Lassing1, Louise Hillberg, Anna-Stina Höglund
1Department of Cell Biology, The Wenner-Gren Institute, Stockholm University, Sweden. ingrid.lassing@wgi.su.se
Cytoskeleton (Hoboken, N.J.)
|July 27, 2010
Summary
Tropomyosin (TM) multimers, not associated with actin filaments, are confirmed to be tetramers. These TM tetramers play a role in actin polymerization dynamics in non-muscle cells.
Area of Science:
- Biochemistry
- Cell Biology
- Structural Biology
Background:
- Tropomyosin (TM) is a coiled-coil dimer crucial for actin filament stability and muscle contraction.
- Non-filamentous TM multimers exist and are involved in actin polymerization and depolymerization.
- The precise structure and size of these non-filamentous TM multimers require elucidation.
Purpose of the Study:
- To determine the size and stoichiometry of non-filamentous tropomyosin multimers.
- To investigate the quaternary structure of native tropomyosin under physiological conditions.
Main Methods:
- Gel-filtration chromatography was employed to assess the Stokes radius of TM.
- Sucrose gradient sedimentation was used to determine the molecular weight of TM.
- Skeletal muscle TM, non-muscle TM isoforms (1 and 5), and TM in cell extracts were analyzed.
Main Results:
- Under physiological salt conditions, TM exhibits a homogeneous peak with a Stokes radius of 8.2 nm and a molecular weight of 130,000.
- These biophysical properties correspond to a tetrameric structure, indicating four TM peptides per multimer.
- Purified non-muscle TM 5 showed similar characteristics, with a Stokes radius of 7.7 nm and a molecular weight of 104,000.
Conclusions:
- Native tropomyosin multimers exist as tetramers.
- These TM tetramers are likely the functional units involved in actin polymerization and depolymerization processes.
- The findings clarify the structural organization of non-filamentous tropomyosin pools.
Related Concept Videos
01:08The Sarcomere
A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each myosin...
Each myosin...
01:16Actin and Myosin in Muscle Contraction
Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...
01:15Overview of Myosin Structure and Function
Myosins are a family of molecular motor proteins, first identified in the skeletal muscles, where they are responsible for muscle contraction. Along with their role in muscle contraction, these proteins also play a role in the intracellular transport of molecules and vesicles. There are twenty-four classes of myosins based on their domain sequence and organization. Of the twenty-four, six classes (Myosin I, Myosin II, Myosin V, Myosin VI, Myosin VII, and Myosin X) have been well characterized.
01:26Cross-bridge Cycle
As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.
01:58Mechanical Protein Functions
Proteins perform many mechanical functions in a cell. These proteins can be classified into two general categories- proteins that generate mechanical forces and proteins that are subjected to mechanical forces. Proteins providing mechanical support to the structure of the cell, such as keratin, are subjected to mechanical force, whereas proteins involved in cell movement and transport of molecules across cell membranes, such as an ion pump, are examples of generating mechanical force.
01:15Overview of Skeletal Muscle
Skeletal muscles are composed of a bundle of muscle fibers and are attached to bones through tendons. Each skeletal muscle fiber is a single muscle cell. The sarcolemma, the plasma membrane of a skeletal muscle cell, consists of a lipid bilayer and glycocalyx that supports muscle fibers. The sarcolemma extends into the muscle cells to form tubular structures called transverse or T-tubules. Each side of the T-tubules consists of a membrane-bound structure called the sarcoplasmic reticulum,...