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spinqualitylabelsall models PDB ID 1c1g Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
1c1g, resolution 7.00Å ()
Structural annotation: Resources: InterPro : Ipr000533 Pfam : PF00261 SCOP : d1c1ga_, d1c1gb_, d1c1gc_, d1c1gd_ UniProt : P42639
Functional annotation: Cellular component: cytoskeleton cytoplasm Molecular function: actin binding
Evolutionary conservation: Toggle Conservation Colors: Rows = identical sequences: Further Information: Caveats, Explanation, Complete Results at ConSurfDB
Resources:	FirstGlance, OCA, RCSB, PDBsum
Coordinates:	save as pdb, mmCIF, xml

Tropomyosin (TM) is an actin binding protein, which consists of a coiled-coil dimer and forms a polymer along the length of actin by a head-to-tail overlap (along the major grove of actin). The head-to-tail overlap allows flexibility between the tropomyosin dimers so it will lay unstrained along the filament.

Its role in muscle mechanics has been well established as it is a major component of the contractile apparatus, but it role in non-muscle systems is becoming evermore clear as there are at least 40 isoforms known in mammals. These isoforms in non-muscle systems, generated by alternative splicing of multiple genes, contribute to actin's stability as well as recruitment of various proteins, including molecular motors.

Contents 1 Structure/Function Relationships 2 Tropomyosin in Muscle Systems 3 Tropomyosin in Non-Muscle Systems 4 Associated Diseases 5 Evolutionary Conservation 6 Solved Tropomyosin Structures 7 References

Structure/Function Relationships

As determined by the Structural Classification of Protein's (SCOP) Database, Tropomyosin is categorized as follows (general to specific):

1. Class: coiled-coil
2. Fold: parallel coiled-coil
3. Superfamily: tropomyosin
4. Family: pig [1c1g]

spinqualitylabelsall models Tropomyosin Dimer Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Categorization of Tropomyosin's coiled-coil motif describes a unique pattern of amino acids within the alpha helices that comprise the dimer interface. This pattern is represented as a helical wheel diagram (see below), whereby the four amino acids (two from each alpha chain) that are adjacent to each other contribute to a , while the four amino acids (two from each alpha chain) flanking the hydrophobic core provide an ionic interaction. Both the hydrophobic and ionic interactions contribute to the stability of the dimer. The hydrophobic amino acids from each alpha chain interact with each other in a knobs in holes packing arrangement, whereby the side chain of an amino acid in one helix fits in between two amino acid side chains of the adjacent helix. This packing allows for the two alpha helices to wrap tightly around each other in a left handed supercoil.

Tropomyosin in Muscle Systems

Muscle tissue is comprised of many muscle fibers or cells. Those muscle fibers consist of myofibrils that contain a series of contractile units called sarcomeres. Within this unit contains thick filaments, comprised mainly of myosin, and thin filaments, which contains actin, tropomyosin and troponin. Tropomyosin in striated muscle systems (skeletal and cardiac) acts to inhibit the myosin cross-bridges from binding to the myosin binding site on actin, this is called the blocked position of tropomyosin. When the muscle is stimulated, there is an eventual rise in intracellular calcium stemming from a cascade of cellular processes. As calcium is bathing the sarcomere, it will bind to the troponin complex, which is bound to both actin and tropomyosin. The troponin will displace the tropomyosin from a "Blocked" to a "Closed" position. This transition allows the myosin head to interact with the myosin binding site on actin weakly. The tropomyosin is displaced to its final position, "Open" state, along actin as myosin binds to its site. These three tropomyosin states along the filament is refered to as the three state model.

Tropomyosin in Non-Muscle Systems

Associated Diseases

Evolutionary Conservation

Solved Tropomyosin Structures

3mtu, 3mud – cTPM alpha-1 – chicken
1ic2 - cTPM alpha-1 (mutant)
2w49, 2w4u – cTnnC+cTnnT+cTnnI+cTPM alpha-1+cActin
2z5h – yTPM alpha-1 N-terminal+C-terminal+GNC4 leucine zipper+TnnT – yeast
2z5i - yTPM alpha-1 N-terminal+C-terminal+GNC4 leucine zipper
2efr, 2efs, 2d3e - rTPM alpha-1 C-terminal+GNC4 leucine zipper – rabbit
1kql - TPM alpha-1 C-terminal+GNC4 leucine zipper - rat
1mv4 - TPM alpha-1 C-terminal – rat
2g9j - TPM alpha-1 TM9A+GNC4 – rat
2b9c – TPM mid region – rat
1c1g – TPM – pig
2tma – TPM - model

References