scholarly journals Troponin T Core Structure and the Regulatory NH2-Terminal Variable Region†

Biochemistry ◽  
2007 ◽  
Vol 46 (5) ◽  
pp. 1368-1379 ◽  
Author(s):  
Brandon J. Biesiadecki ◽  
Stephen M. Chong ◽  
Thomas M. Nosek ◽  
Jian-Ping Jin
Keyword(s):  
Troponin T ◽  
Variable Region ◽  
Core Structure

scholarly journals Nonmyofilament-associated troponin T fragments induce apoptosis

2009 ◽  
Vol 297 (1) ◽  
pp. H283-H292 ◽  
Author(s):  
Euy-Myong Jeong ◽  
Xin Wang ◽  
Kun Xu ◽  
M. Moazzem Hossain ◽  
J.-P. Jin
Keyword(s):  
Fluorescent Protein ◽  
Striated Muscle ◽  
Troponin T ◽  
Variable Region ◽  
Nemaline Myopathy ◽  
Specific Protein ◽  
Cellular Protection ◽  
Cellular Environment ◽  
Nonmuscle Cells ◽  
Green Fluorescent

Troponin T (TnT) is a striated muscle-specific protein and an abundant component of the myofilaments. Nonmyofilament-associated TnT is rapidly degraded in myocytes, implying an importance in the maintenance of the cellular environment. However, if the level of nonmyofilament-associated TnT or TnT fragments exceeds the degradation capacity, it may cause cytotoxicity. To investigate this hypothesis, we constructed bicistronic vectors to express different portions of TnT polypeptide chain, together with nonfusion green fluorescent protein as a tracer for the transfection. Cytotoxicity of the TnT fragments was studied through forced expression in C2C12 myoblasts and human embryonic kidney-293 nonmuscle cells and examination of the viability of the transfected cells. The results demonstrated that, in the absence of myofilaments, the conserved COOH-terminal and middle fragments of TnT were highly effective on inducing cell death via apoptosis, whereas the NH2-terminal variable region was not. As combined effects, nonmyofilament-associated intact cardiac TnT and a COOH-terminal truncated slow TnT fragment found in Amish nemaline myopathy exhibited intermediate cytotoxicity. A particular significance of this finding is that peak releases of TnT or TnT fragments from decomposition of a large number of myofibrils in acute myocardial infarction may breach the cellular protection of proteolytic degradation and result in apoptosis as a potential cause for the loss of cardiomyocytes.

scholarly journals The heart-specific NH2-terminal extension regulates the molecular conformation and function of cardiac troponin I

2012 ◽  
Vol 302 (4) ◽  
pp. H923-H933 ◽  
Author(s):  
Shirin Akhter ◽  
Zhiling Zhang ◽  
J.-P. Jin
Keyword(s):  
Cardiac Troponin ◽  
Troponin I ◽  
Molecular Conformation ◽  
Troponin T ◽  
Cardiac Troponin I ◽  
Core Structure ◽  
Functional Adaptation ◽  
Dependent Manner ◽  
The Core ◽  
And Function

In addition to the core structure conserved in all troponin I isoforms, cardiac troponin I (cTnI) has an ∼30 amino acids NH2-terminal extension. This peptide segment is a heart-specific regulatory structure containing two Ser residues that are substrates of PKA. Under β-adrenergic regulation, phosphorylation of cTnI in the NH2-terminal extension increases the rate of myocardial relaxation. The NH2-terminal extension of cTnI is also removable by restrictive proteolysis to produce functional adaptation to hemodynamic stresses. The molecular mechanism for the NH2-terminal modifications to regulate the function of cTnI is not fully understood. In the present study, we tested a hypothesis that the NH2-terminal extension functions by modulating the conformation of other regions of cTnI. Monoclonal antibody epitope analysis and protein binding experiments demonstrated that deletion of the NH2-terminal segment altered epitopic conformation in the middle, but not COOH-terminal, region of cTnI. PKA phosphorylation produced similar effects. This targeted long-range conformational modulation corresponded to changes in the binding affinities of cTnI for troponin T and for troponin C in a Ca2+-dependent manner. The data suggest that the NH2-terminal extension of cTnI regulates cardiac muscle function through modulating molecular conformation and function of the core structure of cTnI.

Acidic and basic troponin T isoforms in mature fast-twitch skeletal muscle and effect on contractility

1999 ◽  
Vol 276 (5) ◽  
pp. C1162-C1170 ◽  
Author(s):  
Ozgur Ogut ◽  
Henk Granzier ◽  
Jian-Ping Jin
Keyword(s):  
Troponin I ◽  
Striated Muscle ◽  
Troponin T ◽  
Muscle Fibers ◽  
Variable Region ◽  
Breast Muscle ◽  
Chicken Breast ◽  
Adult Chicken ◽  
Isoform Expression ◽  
Fast Twitch

Developmentally regulated alternative RNA splicing generates distinct classes of acidic and basic troponin T (TnT) isoforms. In fast-twitch skeletal muscles, an acidic-to-basic TnT isoform switch ensures basic isoform expression in the adult. As an exception, an acidic segment in the NH2-terminal variable region of adult chicken breast muscle TnT isoforms is responsible for the unique exclusive expression of acidic TnTs in this muscle (O. Ogut and J.-P. Jin. J. Biol. Chem. 273: 27858–27866, 1998). To understand the relationship between acidic vs. basic TnT isoform expression and muscle contraction, the contractile properties of fibers from adult chicken breast muscle were compared with those of the levator coccygeus muscle, which expresses solely basic TnT isoforms. With use of Triton X-100-skinned muscle fibers, the force and stiffness responses to Ca2+ were measured. Relative to the levator coccygeus muscle, the breast muscle fibers showed significantly increased sensitivity to Ca2+ of force and stiffness with a shift of ∼0.15 in the pCa at which force or stiffness was 50% of maximal. The expression of tropomyosin, troponin I, and troponin C isoforms was also determined to delineate their contribution to thin-filament regulation. The data indicate that TnT isoforms differing in their NH2-terminal charge are able to alter the sensitivity of the myofibrillar contractile apparatus to Ca2+. These results provide evidence linking the regulated expression of distinct acidic and basic TnT isoform classes to the contractility of striated muscle.

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