Structural basis for sarcolipin’s regulation of muscle thermogenesis by the sarcoplasmic reticulum Ca
            2+
            -ATPase

The skeletal muscle contractile machine is fueled by both calcium and ATP. Calcium ions activate the contractile machinery by binding to troponin C and relieving troponin-tropomyosin inhibition of actinomyosin interaction. ATP binding to myosin during the contractile cycle results in myosin detachment from actin, and energy liberated from subsequent ATP hydrolysis is then used to drive the next contractile cycle. ATP is also used to lower myoplasmic calcium levels during muscle relaxation. Thus, muscle contractility is intimately linked to the proper control of sarcomeric Ca2+ delivery and (or) removal and ATP generation and (or) utilization. In skeletal muscle, the sarcoplasmic reticulum (SR) is the primary regulator of calcium storage, release, and reuptake, while glycolysis and the mitochondria are responsible for cellular ATP production. However, the SR and mitochondrial function in muscle are not independent, as calcium uptake into the mitochondria increases ATP production by stimulating oxidative phosphorylation and mitochondrial ATP production, and production and (or) detoxification of reactive oxygen and nitrogen species (ROS/RNS), in turn, modulates SR calcium release and reuptake. Close spatial Ca2+/ATP/ROS/RNS communication between the SR and mitochondria is facilitated by the structural attachment of mitochondria to the calcium release unit (CRU) by 10 nm of electron-dense tethers. The resultant anchoring of mitochondria to the CRU provides a structural basis for maintaining bidirectional SR–mitochondrial through-space communication during vigorous contraction. This review will consider the degree to which this structural link enables privileged or microdomain communication between the SR and mitochondria in skeletal muscle.

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Structural basis for relief of the sarcoplasmic reticulum Ca2+-ATPase inhibition by phospholamban at saturating Ca2+ conditions

10.1101/310607 ◽

2018 ◽

Author(s):

Eli Fernández-de Gortari ◽

L. Michel Espinoza-Fonseca

Keyword(s):

Sarcoplasmic Reticulum ◽

Structural Features ◽

Structural Basis ◽

Initial Structure ◽

Structural Mechanism ◽

Cytosolic Side ◽

Dynamics Simulations ◽

Atpase Inhibition ◽

Inhibitory Interactions ◽

Serca Inhibition

AbstractWe have performed extensive atomistic molecular dynamics simulations to probe the structural mechanism for relief of sarcoplasmic reticulum Ca2+-ATPase (SERCA) inhibition by phospholamban (PLB) at saturating Ca2+ conditions. Reversal of SERCA-PLB inhibition by saturating Ca2+ operates as a physiological rheostat to reactivate SERCA function in the absence of PLB phosphorylation. Simulation of the inhibitory complex at super-physiological Ca2+ concentrations ([Ca2+]=10 mM) revealed that calcium ions interact primarily with SERCA and the lipid headgroups, but not with the cytosolic domain of PLB or the cytosolic side of the SERCA-PLB interface. At this [Ca2+], a single Ca2+ ion is translocated from the cytosol to the transmembrane transport sites. We used this Ca2+-bound complex as an initial structure to simulate the effects of saturating Ca2+ at physiological conditions ([Ca2+]total≈400 μM). At these conditions, ~30% of the Ca2+-bound complexes exhibit structural features that correspond to an inhibited state. However, in ~70% of the Ca2+-bound complexes, Ca2+ moves to transport site I, recruits Glu771 and Asp800, and disrupts key inhibitory contacts involving conserved PLB residue Asn34. Structural analysis showed that Ca2+ induces only local changes in interresidue inhibitory interactions, but does not induce dissociation, repositioning or changes in the structural dynamics of PLB. Upon relief of SERCA inhibition, Ca2+ binding produces a productive site I configuration that is sufficient for subsequent SERCA activation. We propose that at saturating [Ca2+] and in the absence of PLB phosphorylation, binding of a single Ca2+ ion in the transport sites rapidly shifts the equilibrium toward a non-inhibited SERCA-PLB complex.

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The Structural Basis for Phospholamban Inhibition of the Calcium Pump in Sarcoplasmic Reticulum

Journal of Biological Chemistry ◽

10.1074/jbc.m113.501585 ◽

2013 ◽

Vol 288 (42) ◽

pp. 30181-30191 ◽

Cited By ~ 77

Author(s):

Brandy L. Akin ◽

Thomas D. Hurley ◽

Zhenhui Chen ◽

Larry R. Jones

Keyword(s):

Sarcoplasmic Reticulum ◽

Calcium Pump ◽

Structural Basis

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The Sarcoplasmic Reticulum and the Evolution of the Vertebrate Heart

Physiology ◽

10.1152/physiol.00015.2014 ◽

2014 ◽

Vol 29 (6) ◽

pp. 456-469 ◽

Cited By ~ 29

Author(s):

Holly A. Shiels ◽

Gina L.J. Galli

Keyword(s):

Sarcoplasmic Reticulum ◽

Structural Organization ◽

Structural Basis ◽

And Function ◽

Contraction And Relaxation ◽

Insight Into

The sarcoplasmic reticulum (SR) is crucial for contraction and relaxation of the mammalian cardiomyocyte, but its role in other vertebrate classes is equivocal. Recent evidence suggests differences in SR function across species may have an underlying structural basis. Here, we discuss how SR recruitment relates to the structural organization of the cardiomyocyte to provide new insight into the evolution of cardiac design and function in vertebrates.

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Structural basis of ion pumping by Ca2+ -ATPase of sarcoplasmic reticulum

FEBS Letters ◽

10.1016/s0014-5793(03)01086-x ◽

2003 ◽

Vol 555 (1) ◽

pp. 106-110 ◽

Cited By ~ 49

Author(s):

Chikashi Toyoshima ◽

Hiromi Nomura ◽

Yuji Sugita

Keyword(s):

Sarcoplasmic Reticulum ◽

Structural Basis ◽

Ion Pumping

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Structural Basis for the Molecular Mechanisms of the Calcium-Transporting ATPase of the Sarcoplasmic Reticulum

New Era of Bioenergetics ◽

10.1016/b978-0-12-509854-0.50007-3 ◽

1991 ◽

pp. 47-72

Author(s):

Masao Kawakita ◽

Yasutada Imamura ◽

Hisanori Yamamoto ◽

Sei-ichi Suzuki ◽

Suguru Kawato

Keyword(s):

Sarcoplasmic Reticulum ◽

Molecular Mechanisms ◽

Structural Basis

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Two Close, Too Close

Circulation Research ◽

10.1161/circresaha.110.225714 ◽

2010 ◽

Vol 107 (6) ◽

pp. 689-699 ◽

Cited By ~ 52

Author(s):

Gerald W. Dorn ◽

Luca Scorrano

Keyword(s):

Sarcoplasmic Reticulum ◽

Molecular Basis ◽

Spatial Organization ◽

Structural Basis ◽

Cell Life ◽

Functional Consequences ◽

Cell Death Cascade ◽

Very High ◽

Present Understanding ◽

Death Signals

Mitochondria are key organelles in cell life whose dysfunction is associated with a variety of diseases. Their crucial role in intermediary metabolism and energy conversion makes them a preferred target in tissues, such as the heart, where the energetic demands are very high. In the cardiomyocyte, the spatial organization of mitochondria favors their interaction with the sarcoplasmic reticulum, thereby offering a mechanism for Ca 2+ -mediated crosstalk between these 2 organelles. Recently, the molecular basis for this interaction has begun to be unraveled, and we are learning how endoplasmic reticulum–mitochondrial interactions are often exploited by death signals, such as proapoptotic Bcl-2 family members, to amplify the cell death cascade. Here, we review our present understanding of the structural basis and the functional consequences of the close interaction between sarcoplasmic reticulum and mitochondria on cardiomyocyte function and death.

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