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Troponin I2, fast skeletal type: The TNNI2 gene provides instructions for making one form of a protein called troponin I.
The TNNI2 gene provides instructions for making one form of a protein called troponin I. The troponin I protein produced from the TNNI2 gene is found in skeletal muscles, which are the muscles used for movement. Troponin I is one of three proteins that make up the troponin complex in muscle cells. The troponin complex, along with calcium, helps regulate muscle tensing (contraction).
The troponin complex is part of a structure called the sarcomere, which is the basic unit of muscle contraction. Sarcomeres contain thick and thin filaments. The overlapping thick and thin filaments attach (bind) to each other and release, which allows the filaments to move relative to one another so that muscles can contract.
When calcium levels are low, the troponin complex blocks the binding between the thick and thin filaments that is needed for muscle contraction. An increase in calcium levels causes structural changes in the troponin complex, which exposes the binding sites and allows the thick and thin filaments to interact, leading to muscle contraction.
At least eight TNNI2 gene mutations have been identified in people with Sheldon-Hall syndrome. This disorder affects muscle and skeletal development before birth and is characterized by joint deformities (contractures) that restrict movement in the hands and feet. Researchers suggest that the TNNI2 gene mutations that cause Sheldon-Hall syndrome may prevent the troponin complex from blocking thick and thin filament binding to control muscle contractions, resulting in the contractures and other muscle and skeletal abnormalities associated with Sheldon-Hall syndrome.