Troponin I and Its Clinical Significance

Troponin I is one of the regulatory proteins of the troponin complex (troponin I, troponin C and troponin T) found in both cardiac and skeletal muscle. The letter I stands for its inhibitory character as binding is prevented between actin and myosin  in relaxed muscle. It plays a significant role in holding actin-tropomyosin complex in place by binding actin in thin myofilaments. Binding of calcium to troponin C causes certain conformational changes, leading to troponin I dislocation and thus exposing binding site of myosin on actin, which leads to muscle contraction. It is frequently used in the diagnosis of acute coronary syndrome and myocardial infarction, and also serves as a prognostic marker in their management (1). There are three distinct forms of troponin I with tissue-specific expression patterns: 1. Slow-twitch skeletal muscle isoform troponin I, 2. Fast-twitch skeletal muscle isoform troponin I and 3. Cardiac troponin I.