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Contribution of the myosin binding protein C motif to functional effects in permeabilized rat trabeculae.

Razumova MV, Bezold KL, Tu AY, Regnier M, Harris SP - J. Gen. Physiol. (2008)

Bottom Line: Myosin binding protein C (MyBP-C) is a thick-filament protein that limits cross-bridge cycling rates and reduces myocyte power output.Recombinant proteins that lacked the combination of C1 and the motif did not affect contractile properties.These results suggest that the C1 domain plus the motif constitute a functional unit of MyBP-C that can activate the thin filament.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Washington, Seattle, WA 98195, USA.

ABSTRACT
Myosin binding protein C (MyBP-C) is a thick-filament protein that limits cross-bridge cycling rates and reduces myocyte power output. To investigate mechanisms by which MyBP-C affects contraction, we assessed effects of recombinant N-terminal domains of cardiac MyBP-C (cMyBP-C) on contractile properties of permeabilized rat cardiac trabeculae. Here, we show that N-terminal fragments of cMyBP-C that contained the first three immunoglobulin domains of cMyBP-C (i.e., C0, C1, and C2) plus the unique linker sequence termed the MyBP-C "motif" or "m-domain" increased Ca(2+) sensitivity of tension and increased rates of tension redevelopment (i.e., k(tr)) at submaximal levels of Ca(2+). At concentrations > or =20 microM, recombinant proteins also activated force in the absence of Ca(2+) and inhibited maximum Ca(2+)-activated force. Recombinant proteins that lacked the combination of C1 and the motif did not affect contractile properties. These results suggest that the C1 domain plus the motif constitute a functional unit of MyBP-C that can activate the thin filament.

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Effects of recombinant N-terminal proteins on rates of tension redevelopment (ktr) relative to changes in force. (A) 5 μM C0C2 (triangles; n = 6) increased ktr to near maximal at all levels of submaximal Ca2+ activation. (B) 5 μM C0C1m (triangles; n = 4) and 5 μM C1C2 (squares; n = 4) increased ktr to near maximal at all levels of submaximal Ca2+ activation, whereas 5 μM C1m (diamonds; n = 6) increased ktr to near maximal only at values at or below the pCa50 for force generation.
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fig7: Effects of recombinant N-terminal proteins on rates of tension redevelopment (ktr) relative to changes in force. (A) 5 μM C0C2 (triangles; n = 6) increased ktr to near maximal at all levels of submaximal Ca2+ activation. (B) 5 μM C0C1m (triangles; n = 4) and 5 μM C1C2 (squares; n = 4) increased ktr to near maximal at all levels of submaximal Ca2+ activation, whereas 5 μM C1m (diamonds; n = 6) increased ktr to near maximal only at values at or below the pCa50 for force generation.

Mentions: To assess whether the motif or C1 affected rates of force activation in addition to their effects on steady-state force–pCa relationships, the rate of force redevelopment after a release and restretch maneuver (i.e., ktr) was measured during each Ca2+ activation. Fig. 6 A shows representative force recordings after a release and restretch protocol for control conditions in the absence of added protein and after incubation of a trabecula with 5 μM C0C2. Incubation with C0C2 significantly accelerated ktr, such that values were near maximal in all pCa solutions (Fig. 6 B). Thus, the Ca2+ dependence of ktr was virtually eliminated by incubation in 5 μM C0C2. Because the rate of tension redevelopment varies as a function of the total level of thin-filament activation (i.e., ktr is increased as a result of both Ca2+ and strongly bound cross-bridges; Gordon et al. [2000]), ktr values were also plotted as a function of the relative force obtained at each pCa. As shown in Fig. 7 A, ktr values measured after incubation with C0C2 were near maximal even at low levels of force. Thus, C0C2 increased ktr to near maximum levels independent of the amount of force generated or, presumably, the number of cycling cross-bridges.


Contribution of the myosin binding protein C motif to functional effects in permeabilized rat trabeculae.

Razumova MV, Bezold KL, Tu AY, Regnier M, Harris SP - J. Gen. Physiol. (2008)

Effects of recombinant N-terminal proteins on rates of tension redevelopment (ktr) relative to changes in force. (A) 5 μM C0C2 (triangles; n = 6) increased ktr to near maximal at all levels of submaximal Ca2+ activation. (B) 5 μM C0C1m (triangles; n = 4) and 5 μM C1C2 (squares; n = 4) increased ktr to near maximal at all levels of submaximal Ca2+ activation, whereas 5 μM C1m (diamonds; n = 6) increased ktr to near maximal only at values at or below the pCa50 for force generation.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2571974&req=5

fig7: Effects of recombinant N-terminal proteins on rates of tension redevelopment (ktr) relative to changes in force. (A) 5 μM C0C2 (triangles; n = 6) increased ktr to near maximal at all levels of submaximal Ca2+ activation. (B) 5 μM C0C1m (triangles; n = 4) and 5 μM C1C2 (squares; n = 4) increased ktr to near maximal at all levels of submaximal Ca2+ activation, whereas 5 μM C1m (diamonds; n = 6) increased ktr to near maximal only at values at or below the pCa50 for force generation.
Mentions: To assess whether the motif or C1 affected rates of force activation in addition to their effects on steady-state force–pCa relationships, the rate of force redevelopment after a release and restretch maneuver (i.e., ktr) was measured during each Ca2+ activation. Fig. 6 A shows representative force recordings after a release and restretch protocol for control conditions in the absence of added protein and after incubation of a trabecula with 5 μM C0C2. Incubation with C0C2 significantly accelerated ktr, such that values were near maximal in all pCa solutions (Fig. 6 B). Thus, the Ca2+ dependence of ktr was virtually eliminated by incubation in 5 μM C0C2. Because the rate of tension redevelopment varies as a function of the total level of thin-filament activation (i.e., ktr is increased as a result of both Ca2+ and strongly bound cross-bridges; Gordon et al. [2000]), ktr values were also plotted as a function of the relative force obtained at each pCa. As shown in Fig. 7 A, ktr values measured after incubation with C0C2 were near maximal even at low levels of force. Thus, C0C2 increased ktr to near maximum levels independent of the amount of force generated or, presumably, the number of cycling cross-bridges.

Bottom Line: Myosin binding protein C (MyBP-C) is a thick-filament protein that limits cross-bridge cycling rates and reduces myocyte power output.Recombinant proteins that lacked the combination of C1 and the motif did not affect contractile properties.These results suggest that the C1 domain plus the motif constitute a functional unit of MyBP-C that can activate the thin filament.

View Article: PubMed Central - PubMed

Affiliation: Department of Bioengineering, University of Washington, Seattle, WA 98195, USA.

ABSTRACT
Myosin binding protein C (MyBP-C) is a thick-filament protein that limits cross-bridge cycling rates and reduces myocyte power output. To investigate mechanisms by which MyBP-C affects contraction, we assessed effects of recombinant N-terminal domains of cardiac MyBP-C (cMyBP-C) on contractile properties of permeabilized rat cardiac trabeculae. Here, we show that N-terminal fragments of cMyBP-C that contained the first three immunoglobulin domains of cMyBP-C (i.e., C0, C1, and C2) plus the unique linker sequence termed the MyBP-C "motif" or "m-domain" increased Ca(2+) sensitivity of tension and increased rates of tension redevelopment (i.e., k(tr)) at submaximal levels of Ca(2+). At concentrations > or =20 microM, recombinant proteins also activated force in the absence of Ca(2+) and inhibited maximum Ca(2+)-activated force. Recombinant proteins that lacked the combination of C1 and the motif did not affect contractile properties. These results suggest that the C1 domain plus the motif constitute a functional unit of MyBP-C that can activate the thin filament.

Show MeSH
Related in: MedlinePlus