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. Author manuscript; available in PMC: 2024 Mar 11.
Published in final edited form as: J Mol Evol. 2021 Dec 29;90(1):30–43. doi: 10.1007/s00239-021-10039-9

Fig. 3. Cardiac TnI has evolved with a unique additional N-terminal extension.

Fig. 3.

A, The linear protein maps illustrate that while the core structure of the three muscle type TnI isoforms is highly conserved, the N-terminal extension of cardiac TnI is an additional structure that is absent from the skeletal muscle isoforms. The N-terminal extension of cardiac TnI is a regulatory structure containing PKA phosphorylation sites Ser23 and Ser24. B, Phylogenetic lineage analysis showed that in contrast to the fast TnI, cardiac TnI and slow TnI from bony fishes show high degrees of similarity and grouped together, suggesting the emergence of vertebrate cardiac TnI in primordial fishes.