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Troponin I, fast skeletal muscle is a protein that in humans is encoded by the ''TNNI2'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=7136 )〕 The TNNI2 gene is located at 11p15.5 in the human chromosomal genome, encoding the fast twitch skeletal muscle troponin I (fsTnI). fsTnI is a 21.3 kDa protein consisting of 182 amino acids including the first methionine with an isoelectric point (pI) of 8.74. It is the inhibitory subunit of the troponin complex in fast twitch skeletal muscle fibers. == Gene evolution == Three homologous genes have evolved in vertebrates, encoding three muscle type-specific isoforms of TnI. Sequence analysis, immunological distance, and examination of evolutionarily suppressed conformational states showed that the TnI genes have evolved in close linkage with the genes encoding troponin T (TnT), another subunit of the troponin complex.〔 The fast TnI-fast TnT gene pair represents the original TnI and TnT genes (Fig. 1). The three muscle fiber type-specific TnI-TnT gene pairs were likely originated from a TnI-like ancestor gene that presumably duplicated to form a closely linked fast TnI-like and fast TnT-like gene pair. A later duplication events resulted in emergences of a slow TnI-like and cardiac TnT-like gene pair that was further duplicated to give rise of the present-day slow TnI-cardiac TnT and cardiac TnI-slow TnT gene pairs. The seemingly scrambled ssTnI and cTnI gene pair is actually functionally related as they co-express and form troponin complex in the embryonic heart. The overlapping of enhancer elements of the TnT gene promoter with the upstream TnI gene structure may be a critical factor in the preservation of the close linkage of TnI and TnT gene pairs The phylogenetic tree in Fig. 2 summarizes the evolutionary lineage of fsTnI isoforms in vertebrate species. Phylogenetic analysis of vertebrate TnI isoforms demonstrated that each of the muscle type-specific isoforms is more conserved across species than the three isoforms in one given species, indicating early diverged functions of the muscle fiber type-specific isoforms as well as the conservation of functions for each muscle fiber type. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「TNNI2」の詳細全文を読む スポンサード リンク
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