Figure 6. Molecular mechanisms of sarcomere activation.

Figure 6

Molecular mechanisms of sarcomere activation. The left panel shows the diastolic state of a region of overlap of thin and thick filaments illustrating detailed structure and location of major protein strands consisting of actin and tropomyosin (Tm). Attached to the thin filament is a the heterotrimeric troponin (Tn) complex. TnC is a dumbbell shaped protein with the N-lobe containing a single regulatory Ca-binding site. cTnI is shown tethered to actin on an actin strand by an inhibitory peptide and a second actin binding region flanking a switch peptide, which interacts with cTnC upon Ca-activation. cTnI has a unique stretch of N-terminal amino acids, which contain phosphorylation sites at S23, S24. The N-peptide interacts with the N-lobe of cTnC, but is released upon phosphorylation. Tm is wedged and immobile in a position that blocks the actin –cross-bridge reaction. Tm is held in this blocking position by the Ip of cTnI on one side, and by the N-terminal tail of troponin T (cTnT) from the Tn in register on the adjacent actin strand. cTnT from the Tn complex on the adjacent actin strand is shown with stripes. The right panel shows Ca2+-binding to TnC that triggers alterations in thin filament structure and promotion of the actin-cross-bridge reaction. Myosin binding protein C (MyB-C) and myosin light chains (MLC1 and MLC2) modulate cross-bridge activity. Titin is a major structural protein responsible for passive tension. (See text for further discussion).

From: Left Ventricular Diastolic and Systolic Pressure, Ejection, and Relaxation Reflect Sarcomeric Mechanical Properties

Cover of Regulation of Cardiac Contractility
Regulation of Cardiac Contractility.
Solaro RJ.
San Rafael (CA): Morgan & Claypool Life Sciences; 2011.
Copyright © 2011 by Morgan & Claypool Life Sciences.

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