Properties of single chloride selective channel from sarcoplasmic reticulum

Rousseau, Éric; Roberson, Mya L.; Meissner, Gerhard

doi:10.1007/bf00261900

Cited by 43 publications

(30 citation statements)

References 39 publications

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“…During Ca 2ϩ movement across the SR membrane, an equivalent amount of counterions (e.g., the ubiquitous Cl Ϫ ) must cross the membrane to maintain electro-neutrality. A number of research groups have measured chloride currents in the SR (41,42), but a Cl Ϫ channel of the SR membrane is yet to be identified. It is interesting to note in this context that in one chloride conductance study, monoclonal anti-PLN antibody abolished chloride current across the membrane of SR-derived vesicles (43).…”

Section: Fig 2 Intermonomer Distance Restraints (A)mentioning

confidence: 99%

The structure of phospholamban pentamer reveals a channel-like architecture in membranes

Oxenoid

Chou

2005

Proc. Natl. Acad. Sci. U.S.A.

295

381

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Contraction and relaxation of heart muscle cells is regulated by cycling of calcium between cytoplasm and sarcoplasmic reticulum. Human phospholamban (PLN), expressed in the sarcoplasmic reticulum membrane as a 30-kDa homopentamer, controls cellular calcium levels by a mechanism that depends on its phosphorylation. Since PLN was discovered Ϸ30 years ago, extensive studies have aimed to explain how it influences calcium pumps and to determine whether it acts as an ion channel. We have determined by solution NMR methods the atomic resolution structure of an unphosphorylated PLN pentamer in dodecylphosphocholine micelles. The unusual bellflower-like assembly is held together by leucine͞isoleucine zipper motifs along the membrane-spanning helices. The structure reveals a channel-forming architecture that could allow passage of small ions. The central pore gradually widens toward the cytoplasmic end as the transmembrane helices twist around each other and bend outward. The dynamic Nterminal amphipathic helices point away from the membrane, perhaps facilitating recognition and inhibition of the calcium pump.leucine͞isoleucine zipper ͉ membrane channel ͉ NMR ͉ dipolar couplings P hospholamban (PLN) in the sarcoplasmic reticulum (SR) membrane of cardiomyocytes regulates the level of intracellular calcium, the main determinant of muscle contraction and relaxation. In the unphosphorylated form, PLN has an inhibitory effect on the sarco(endo)plasmic reticulum calcium ATPase (SERCA), a membrane protein responsible for pumping most of the calcium from the cytoplasm into the SR, thereby causing relaxation of myofibrils. Heart stimulants, such as adrenaline, set off a chain of signal transduction events that among other effects lead to PLN phosphorylation. Phosphorylated PLN no longer inhibits SERCA, allowing for more efficient pumping of calcium. Imbalance in the PLN-SERCA interaction leads to deterioration of heart function and cardiomyopathy (1). In vitro experiments have suggested that SERCA binds PLN by stripping a subunit away from the unphosphorylated 30-kDa pentamer, thereby depolymerizing PLN assembly (2, 3), but the nature of this interaction is still not understood. In addition to its role as a calcium pump regulator, there have been early ion conductance studies suggesting that PLN is also an ion channel (4). This hypothesis has not been tested further due in part to the lack of structural information on the PLN pentamer.To elucidate a potential dual function of PLN, we have determined the structure of the unphosphorylated human PLN pentamer by solution NMR methods at 30°C and compared it with that of a monomeric mutant (5). The pentamer structure reveals a number of previously undescribed features. The unusual axial orientation and flexibility of the extramembrane helices in the pentamer may facilitate recognition by SERCA, whereas the supercoiling and bending of the membrane-spanning helices leads to formation of a funnel-like channel with a hydrophobic neck, as in many known ion channels. MethodsProtein Preparat...

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Section: Fig 2 Intermonomer Distance Restraints (A)mentioning

confidence: 99%

The structure of phospholamban pentamer reveals a channel-like architecture in membranes

Oxenoid

Chou

2005

Proc. Natl. Acad. Sci. U.S.A.

295

381

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“…Such studies are not possible for ryanodine receptor-channels in the native SR, as the membrane also contains monovalent cation- (Miller, 1978;Tomlins, Williams & Montgomery, 1984) and anion-selective (Tanifuji, Sokabe & Kasai, 1987;Rousseau, Roberson & Meissner, 1988;Holmberg & Williams, 1989) channels. Preliminary studies have established that the pure ryanodine receptor-channels of both skeletal (Lai et al 1988 a;Smith et al 1988;Ma et al 1988;Liu, Lai, Rousseau, Jones & Meissner, 1989) and cardiac (Lai et al 1988b;Anderson et at.…”

Section: Introductionmentioning

confidence: 99%

Monovalent cation conductance in the ryanodine receptor‐channel of sheep cardiac muscle sarcoplasmic reticulum.

Lindsay

Manning

Williams

1991

The Journal of Physiology

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SUMMARY1. The ryanodine receptor protein of sheep cardiac muscle sarcoplasmic reticulum membranes functions as a ligand-regulated ion channel following solubilization with the zwitterionic detergent CHAPS (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulphonate); purification by density gradient centrifugation, reconstitution into proteo-liposomes and incorporation into planar phospholipid bilayers.2. In the absence of divalent cations, measurable conductance is observed with the group la cations and with some larger organic cations. In symmetric 210 mM solutions the following conductance sequence was determined: K+ > Rb+ NH4+ > Na+ = Cs+ > Li+ > Tris+.3. Other organic cations, e.g. TEA+, do not produce measurable current under these conditions. 4. Single-channel conductance saturates with increasing ionic activities of K+, Na+ and Li+. Saturation curves are described by Michaelis-Menten kinetic schemes with the following values of maximal conductance and apparent dissociation constant: K+ 900 pS, 19-9 mM; Na+ 516 pS, 17-8 mM; Li' 248 pS, 9-1 mM.5. The channel displays only minor differences in permeability amongst the group la cations. Relative permeability, monitored under bi-ionic conditions, yields the following sequence: Na+, 1-15 > K+, 1-00 = Li+, 0 99 > Rb+, 0-87 > Cs+, 0-61. Under similar conditions the permeability ratio of NH4+ to K+ was found to be 1-32 and that for Tris+ to K+ was 0-22.6. The K+ conductance is reduced by low concentrations of the impermeant cation TEA+. Block appears as a smooth reduction in single-channel current amplitude and the degree of block is dependent upon applied voltage. These observations are consistent with a single-site blocking scheme in which TEA+ has access to a site within the voltage drop of the channel from only the cytosolic face of the channel protein and interacts with a site located approximately 90% of the electrical distance across the channel. The zero-voltage dissociation constant for TEA+ block is 50 mM.7. Single-channel conductance measurements in mixtures of K+-Na+ and K+-Li+ reveal no anomalous behaviour as the mole fraction of the ions is varied.8

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“…In mammalian skeletal SR preparations, a K+ channel and a Clchannel have been studied (Miller et al, 1984;Rousseau et al, 1988). Miller and Racker (1976) successfully developed a technique for fusing SR vesicles into an artificial membrane and studying the characteristics of channel proteins of the SR membrane.…”

Section: Monovalent Channels Present In the Srmentioning

confidence: 99%

Modification of the CA²⁺ Release Channel from Sarcoplasmic Reticulum of Skeletal Muscle

Xiong¹

2000

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Properties of single chloride selective channel from sarcoplasmic reticulum

Cited by 43 publications

References 39 publications

The structure of phospholamban pentamer reveals a channel-like architecture in membranes

The structure of phospholamban pentamer reveals a channel-like architecture in membranes

Monovalent cation conductance in the ryanodine receptor‐channel of sheep cardiac muscle sarcoplasmic reticulum.

Modification of the CA²⁺ Release Channel from Sarcoplasmic Reticulum of Skeletal Muscle

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