Troponin T Core Structure and the Regulatory Nh2-terminal Variable Region.
From: Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA.
Biochemistry
- Publish Date: Feb 2007
- ISSN: 0006-2960
- Volume: 46
- Issue: 5
- Pages: 1368-79
- Medium: Print
- Language: English
- Citation (JAMA): Biesiadecki Brandon J, Chong Stephen M, Nosek Thomas M, et al. Troponin T Core Structure and the Regulatory Nh2-terminal Variable Region.. Biochemistry Feb 2007;46:1368-79
Abstract
The conserved central and COOH-terminal regions of troponin T (TnT) interact with troponin C, troponin I, and tropomyosin to regulate striated muscle contraction. Phylogenic data show that the NH2-terminal region has evolved as an addition to the conserved core structure of TnT. This NH2-terminal region does not bind other thin filament proteins, and its sequence is hypervariable between fiber type and developmental isoforms. Previous studies have demonstrated that NH2-terminal modifications alter the COOH-terminal conformation of TnT and thin filament Ca2+-activation, yet the functional core structure of TnT and the mechanism of NH2-terminal modulation are not well understood. To define the TnT core structure and investigate the regulatory role of the NH2-terminal variable region, we investigated two classes of model TnT molecules: (1) NH2-terminal truncated cardiac TnT and (2) chimera proteins consisting of an acidic or basic skeletal muscle TnT NH2-terminus spliced to the cardiac TnT core. Deletion of the TnT hypervariable NH2-terminus preserved binding to troponin I and tropomyosin and sustained cardiac muscle contraction in the heart of transgenic mice. Further deletion of the conserved central region diminished binding to tropomyosin. The reintroduction of differently charged NH2-terminal domains in the chimeric molecules produced long-range conformational changes in the central and COOH-terminal regions to alter troponin I and tropomyosin binding. Similar NH2-terminal charge effects are demonstrated in naturally occurring cardiac TnT isoforms, indicating a physiological significance. These results suggest that the hypervariable NH2-terminal region modulates the conformation and function of the TnT core structure to fine-tune muscle contractility.
Mesh Headings (Keywords): Amino Acid Sequence, Animals, Mice, Mice, Transgenic, Muscle Contraction, Myocardial Contraction, Protein Binding, Protein Conformation, Tropomyosin, Troponin C, Troponin I, Troponin T
Check for Full Text / PubMed Unique Identifier (PMID): 17260966
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